**Quality Control of Ionizing Radiation in Radiotherapy**

Ernesto Lamanna, Bianco Cataldo, Giulia Marvaso, Marco D'Andrea and Lidia Strigari

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60421

#### **Abstract**

[77] Thor M, Apte A, Deasy JO, Karlsdóttir À, Moiseenko V, Liu M, et al. Dose/volume– response relations for rectal morbidity using planned and simulated motion-inclu‐

[78] Comparison of linac-based fractionated stereotactic radiotherapy and tomotherapy treatment plans for intra-cranial tumors, Jang Bo Shim, Suk Lee, Sam Ju Cho, Sang Hoon Lee, Juree Kim, Kwang Hwan Cho, ChulKee Min, Hyun Do Huh, Rena Lee, DaeSik Yang, Young Je Park, Won Seob Yoon, Chul Yong Kim, Soo Il Kwon, Chinese

[79] Optimization of beam orientation and virtual organ delineation for lung IMRT, Kyung Hwan Chang, Suk Lee, Yuan Jie Cao, Jang Bo Shim, Ji Eun Lee, Nam Kwon Lee, Jung Ae Lee, DaeSik Yang, Young Je Park, Won Sup Yoon, and Chul Yong Kim, Sam Ju Cho, Sang Hoon Lee, Woo Chul Kim, ChulKee Min, Kwang Hwan Cho, Hy‐ un Do Huh, Journal of the Korean Physical Society, Volume 64, Issue 7, 1047-1054,

[80] Patient performance-based plan parameter optimization for prostate cancer in tomo‐ therapy, Yuan Jie Cao, Suk Lee, Kyung Hwan Chang, Jang Bo Shim, KwangHyeon

[81] Optimized planning target volume margin in helical tomotherapy for prostate can‐ cer: is there a preferred method?, Yuan Jie Cao, Suk Lee, Kyung Hwan Chang, Jang Bo Shim, KwangHyeon Kim, et al., Journal of the Korean Physical Society, 67(1),

[82] Dosimetrical and radiobiological comparison of intensity modulated planning tech‐ niques for prostate radiotherapy: a multi-institutional study, Suk Lee, Yuan Jie Cao, Kyung Hwan Chang, Jang Bo Shim, KwangHyeon Kim, et al., Journal of the Korean

sive dose distributions. Radiotherapy and Oncology. 2013; 109(3):388–93.

Physics C, 34(11): 1768-1774, Nov., 2010

Physical Society, 2015, article in press.

Kim, et al., Medical Dosimetry, 2015, article in press.

2014 (SCI, 0.476)

150 Evolution of Ionizing Radiation Research

26-32, 2015

This work includes the results of our research on the measurement of the dose delivered by an external beam in radiotherapy. The use of scintillating fibers in highenergy experiments produced rapid and reliable results and allows new dosimeters to be built and extends their use to measure the dose of an external beam of electrons, photons, and hadrons in radiotherapy.The chapter starts from the description of the radiation used in radiotherapy, presents the new approaches and then the tools used to perform the quality control of therapeutic beams, and finally shows the character‐ istics and differences compared to the traditional quality controls by using our results on the scintillating fibers used as a dosimeter. Some care should be taken into account during the collection and processing of data, for the treatment of some systematic errors in the method. In this chapter, we describe the procedure to be followed.

**Keywords:** radiotherapy, IMRT, dosimeter, scintillating fibers

#### **1. Introduction**

The use of ionizing radiation for the treatment of cancer can be traced back to the discovery of X-rays and radioactive isotopes by WC Roentgen (1895), H. Becquerel (1896), and M. and P. Curie (1898). X-rays have been used in clinical medicine since the early years of the twentieth century [1]. Initially, X-rays used energies required for diagnostic purposes and then higher energies (180–200 kV) of the photons produced by X-ray tubes developed to treat tumors. The ability to treat tumors located in deeper tissues was guaranteed later by the development in

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the 1950s of linear accelerators of electrons with energies of 4–20 MeV and the production of intense beams of photons with delivery of higher doses [2]. The most important limitation to their use was the excessive radiation in normal tissue surrounding the tumors. To overcome this, the approach of multifield treatment plans has been developed to guarantee the dose necessary for the tumor, thus reducing the high dose to normal tissues. In the same years, the technology developed to produce accelerators of massive particles allowed therapeutic trials of protons and ions to kill cancer cells to be started [3]. The development of more powerful computers allowed treatment plans to be set up with the assistance of the computer, and from 1984, excellent treatment systems with beams of protons and ions for clinical use were realized. The method of treatment with protons and ions is advantageous for its characteristic of maximum energy transfer near the stopping point of the particle. Using electrons or photons the dose delivered is continuously reduced by increasing its depth. For this reason, hadron beams are preferable for deep tumors. Currently, the systems required for the use of hadrons are expensive, and there are few centers in the world in which they are available [4]. The systems that produce beams of electrons and photons are cheaper and have spread widely in health facilities. They are referred to as "conventional radiotherapy." Research for the im‐ provement of their use has produced an impact on the treatment method by introducing new ways to deliver the dose: the intensity-modulated radiation therapy (IMRT) and the volumet‐ ric-modulated arc therapy (VMAT). The new methodologies require more accurate detectors for measuring the dose delivered and for assuring quality controls of the system used, with high spatial and temporal resolutions.

#### **2. Ionizing radiation used in radiotherapy**

Radiotherapy, also called radiation therapy (RT), indicates the treatment of cancer and other diseases with ionizing radiation, which are used to deposit energy in tumor cells and directly or indirectly damage the genetic material (DNA) in the individual cells, making it impossible for them to continue to grow.

One type of radiation therapy commonly used is with photons, "packets" of energy, or particles, which, depending on the amount of energy they possess, destroy cancer cells on the surface of an area or penetrate to tissues deeper in the body. The higher the energy of the photon beam, the deeper the distance at which a given dose is delivered into the target tissue.

Linear accelerators are generally adopted in Radiotherapy departments to focus ionizing radiation on a cancer site, and this modality is called external beam radiotherapy (EBR). With modern radiation equipment, the radiation is focused on the target thanks to a multileaf collimator (MLC) and a complex sequence of their movements aimed at delivering conformal dose distribution using static or dynamic position of leaves at different static or dynamic gantry positions.

All the above delivery modalities are potentially associated to an on board imaging device in order to improve the treatment setup reproducibility, thanks to 2D/3D imaging based on kV or MV-based imaging.

the 1950s of linear accelerators of electrons with energies of 4–20 MeV and the production of intense beams of photons with delivery of higher doses [2]. The most important limitation to their use was the excessive radiation in normal tissue surrounding the tumors. To overcome this, the approach of multifield treatment plans has been developed to guarantee the dose necessary for the tumor, thus reducing the high dose to normal tissues. In the same years, the technology developed to produce accelerators of massive particles allowed therapeutic trials of protons and ions to kill cancer cells to be started [3]. The development of more powerful computers allowed treatment plans to be set up with the assistance of the computer, and from 1984, excellent treatment systems with beams of protons and ions for clinical use were realized. The method of treatment with protons and ions is advantageous for its characteristic of maximum energy transfer near the stopping point of the particle. Using electrons or photons the dose delivered is continuously reduced by increasing its depth. For this reason, hadron beams are preferable for deep tumors. Currently, the systems required for the use of hadrons are expensive, and there are few centers in the world in which they are available [4]. The systems that produce beams of electrons and photons are cheaper and have spread widely in health facilities. They are referred to as "conventional radiotherapy." Research for the im‐ provement of their use has produced an impact on the treatment method by introducing new ways to deliver the dose: the intensity-modulated radiation therapy (IMRT) and the volumet‐ ric-modulated arc therapy (VMAT). The new methodologies require more accurate detectors for measuring the dose delivered and for assuring quality controls of the system used, with

Radiotherapy, also called radiation therapy (RT), indicates the treatment of cancer and other diseases with ionizing radiation, which are used to deposit energy in tumor cells and directly or indirectly damage the genetic material (DNA) in the individual cells, making it impossible

One type of radiation therapy commonly used is with photons, "packets" of energy, or particles, which, depending on the amount of energy they possess, destroy cancer cells on the surface of an area or penetrate to tissues deeper in the body. The higher the energy of the photon beam, the deeper the distance at which a given dose is delivered into the target tissue.

Linear accelerators are generally adopted in Radiotherapy departments to focus ionizing radiation on a cancer site, and this modality is called external beam radiotherapy (EBR). With modern radiation equipment, the radiation is focused on the target thanks to a multileaf collimator (MLC) and a complex sequence of their movements aimed at delivering conformal dose distribution using static or dynamic position of leaves at different static or dynamic gantry

high spatial and temporal resolutions.

152 Evolution of Ionizing Radiation Research

for them to continue to grow.

positions.

**2. Ionizing radiation used in radiotherapy**

In fact, in radiation therapy, a sharply defined dose distribution minimizes the side effects of treatment because only small amounts of radiation travel to the surrounding tissues. Gamma rays are produced spontaneously as certain elements (such as cobalt 60) release radiation as they decompose, or decay and are another form of photons used in radiotherapy. Each element decays at a specific rate and gives off energy in the form of gamma rays and other particles.

Another technique for delivering radiation to cancer cells relies on the possibility of placing radioactive implants directly into a tumor or body cavity and are denoted as brachytherapy, interstitial, or intracavity irradiation. This technique is also called internal radiotherapy, and it is appreciated because it is able to deliver high doses concentrated in a small area, generating a high-dose gradient. Internal radiotherapy is sometimes used for cancers of the tongue, uterus, prostate, and cervix but in some cases is considered an invasive procedure.

Other proposed approaches include intraoperative irradiation, in which a large dose of external radiation is directed on to the tumor or tumor bed during surgery, thanks to conven‐ tional use of dedicated mobile linear accelerators. Other investigational techniques include the particle beam radiation therapy based on the acceleration of proton or ions to treat localized cancers. The acceleration of these particles requires very sophisticated machines generating modulated or conformal beams to damage tumor cells. Several of these particles, depending on their energy, could produce damage radiobiologically more efficacious than conventional radiotherapy on both tumor and normal tissues, the latter spared by using very conformal dose distributions.

Other recent radiotherapy modalities are based on radiolabeled antibodies to deliver doses of radiation directly to the cancer site due the presence of tumor-specific antibodies (radioim‐ munotherapy) or in general radionuclides, which thank to their chemical features or their direct injection in the target tissue/tumor bed can target more precisely. The success of this technique will depend upon both the identification of appropriate radioactive substances and the determination of the safe and effective dose of radiation that can be delivered in this way.

Scientists are also looking for ways to increase the effectiveness of existing radiation therapy techniques, based on investigational drugs including radiosensitizers, which make the tumor cells more likely to be damaged, radioprotectors, which protect normal tissues from the effects of radiation, or anti-angiogenic drug, interfering with the neo-angiogenic process. Hyperther‐ mia, or the use of heat, is also being studied for its effectiveness in sensitizing tissues to radiation.

#### **3. New methodology in radiotherapy**

Radiation therapy (RT) is an integrated part of the modern comprehensive cancer manage‐ ment. Radiotherapy has seen continuous technological improvements since the discovery of X-rays in 1895 [5]. The main focus in radiation therapy has always been to increase the level of precision and accuracy of dose delivery to the tumor target volume while sparing normal tissue. Remarkable progress has been made in this area, which is especially based on the new delivery systems, new imaging modalities, and more powerful computers and software. These include, for external beam radiotherapy (EBR), the development of advanced linear accelera‐ tors, with higher energies and better dose characteristics and skin sparing, as well as smaller sources for reduced lateral penumbra, which date back to the 1950s [6]. One of the major advances in radiation oncology in the early 1990s was the application of computer-graphics technology to CT scanning, when 2D RT was largely replaced by 3D RT, based on CT imaging. Furthermore, radiation dosimetry based on 3D conformal therapy has been studied more accurately, and Monte Carlo methodology [7] has been also introduced into the current calculation for patient dosimetry. Based on EBTR approach, in the first few years of this century, the next technical step forward consisted of the great interest generated in another form of conformal treatment planning, that is, intensity-modulated radiation therapy (IMRT). IMRT allowed better conformation around the tumor and surrounding normal tissue, involving the delivery of optimized, nonuniform irradiation beam intensities. A uniform dose distribution can be created around the tumor by either modulating the intensity of the beam during its journey through the linear accelerator or by using multileaf collimators (MLCs). IMRT is now available in many clinical departments and can be delivered by linear accelerators with smaller segments of differing MLC shape, such as in the case of static IMRT, or modulated by continuously moving MLC, such as in the case of dynamic IMRT [8]. Other derived techniques include tomotherapy, which uses a dedicated CT scan unit and is well suited to treat large volumes [9]. This has led to improvements in the therapeutic ratio for several tumor sites, such as head and neck [10], prostate [11], and gynecological cancers [12]. Volumetricmodulated arc therapy (VMAT) is an advanced form of IMRT that can be delivered using conventional linear accelerators with conventional MLC. VMAT can provide highly conformal dose distribution and improve the IMRT delivery efficiency significantly. The basic concept of arc therapy is the delivery of radiation by means of a continuous rotation of the radiation source and allows the patient to be treated from a full 360 beam angle. However, a major advantage over fixed gantry IMRT is the improvement in treatment delivery efficiency, as a result of the reduction in treatment delivery time and the reduction in monitor unit (MU) usage, with subsequent reduction of integral radiation dose to the rest of the body [13, 14]. In the last decade, there has been a very rapid growth in the clinical application of stereotactic radiosur‐ gery (SRS) and stereotactic body radiation therapy (SBRT). Although the first stereotactic devices were designed by Leksell [15] for the treatment of intracranial benign or malignant lesions, and this was the primary indication, technical improvements in SBRT planning have allowed its use for extracranial lesions [16]. Stereotactic treatment requires strict immobiliza‐ tion, advanced image guidance, and sophisticated treatment planning and delivery systems, resulting in highly conformal dose distributions that allow decreases in the size of treatment volumes relative to conventional radiotherapy. This, in turn, allows for delivery of large doses of radiation per fraction and increased biologically effective doses (BED) beyond those possible with conventional treatments.

#### **4. Quality control and dosimetry of the beam**

X-rays in 1895 [5]. The main focus in radiation therapy has always been to increase the level of precision and accuracy of dose delivery to the tumor target volume while sparing normal tissue. Remarkable progress has been made in this area, which is especially based on the new delivery systems, new imaging modalities, and more powerful computers and software. These include, for external beam radiotherapy (EBR), the development of advanced linear accelera‐ tors, with higher energies and better dose characteristics and skin sparing, as well as smaller sources for reduced lateral penumbra, which date back to the 1950s [6]. One of the major advances in radiation oncology in the early 1990s was the application of computer-graphics technology to CT scanning, when 2D RT was largely replaced by 3D RT, based on CT imaging. Furthermore, radiation dosimetry based on 3D conformal therapy has been studied more accurately, and Monte Carlo methodology [7] has been also introduced into the current calculation for patient dosimetry. Based on EBTR approach, in the first few years of this century, the next technical step forward consisted of the great interest generated in another form of conformal treatment planning, that is, intensity-modulated radiation therapy (IMRT). IMRT allowed better conformation around the tumor and surrounding normal tissue, involving the delivery of optimized, nonuniform irradiation beam intensities. A uniform dose distribution can be created around the tumor by either modulating the intensity of the beam during its journey through the linear accelerator or by using multileaf collimators (MLCs). IMRT is now available in many clinical departments and can be delivered by linear accelerators with smaller segments of differing MLC shape, such as in the case of static IMRT, or modulated by continuously moving MLC, such as in the case of dynamic IMRT [8]. Other derived techniques include tomotherapy, which uses a dedicated CT scan unit and is well suited to treat large volumes [9]. This has led to improvements in the therapeutic ratio for several tumor sites, such as head and neck [10], prostate [11], and gynecological cancers [12]. Volumetricmodulated arc therapy (VMAT) is an advanced form of IMRT that can be delivered using conventional linear accelerators with conventional MLC. VMAT can provide highly conformal dose distribution and improve the IMRT delivery efficiency significantly. The basic concept of arc therapy is the delivery of radiation by means of a continuous rotation of the radiation source and allows the patient to be treated from a full 360 beam angle. However, a major advantage over fixed gantry IMRT is the improvement in treatment delivery efficiency, as a result of the reduction in treatment delivery time and the reduction in monitor unit (MU) usage, with subsequent reduction of integral radiation dose to the rest of the body [13, 14]. In the last decade, there has been a very rapid growth in the clinical application of stereotactic radiosur‐ gery (SRS) and stereotactic body radiation therapy (SBRT). Although the first stereotactic devices were designed by Leksell [15] for the treatment of intracranial benign or malignant lesions, and this was the primary indication, technical improvements in SBRT planning have allowed its use for extracranial lesions [16]. Stereotactic treatment requires strict immobiliza‐ tion, advanced image guidance, and sophisticated treatment planning and delivery systems, resulting in highly conformal dose distributions that allow decreases in the size of treatment volumes relative to conventional radiotherapy. This, in turn, allows for delivery of large doses of radiation per fraction and increased biologically effective doses (BED) beyond those possible

with conventional treatments.

154 Evolution of Ionizing Radiation Research

IMRT and VMAT treatments are extremely complex and require patients' specific quality assurance be performed to ensure the dose calculated by treatment planning systems to be the actual dose delivered to the patient at the treatment unit. Guidelines for IMRT commissioning have been published by AAPM Task Group (TG) 119 [17]. The guidelines established test cases to benchmark the overall accuracy of IMRT planning and delivery. The AAPM TG 119 relies on two preliminary tests to evaluate a dose calculating module and four commissioning cases: test prostate, head and neck (H&N), C-shaped target, and multitarget [17].

Typically, IMRT patient-specific QA is performed on a linac using a homogeneous phantom and a dose-measuring device to measure the absolute dose in representative points in the phantom or planar doses. This method requires time on a linac and increases the workload for medical physicist staff. Unfortunately, it is difficult to replicate patient geometries and heterogeneity using a phantom-based QA method.

Treatment plan QA software has been proposed to act as an independent plan evaluation and dosimetry check, thus removing the need to carry out measurements. Unfortunately, this method does not take into account potential failure during delivery that could affect the expected fluence flow map generated by linac.

VMAT [14] is an arc-based IMRT to be delivered on a conventional linac provided of MLC. During arc beam delivery, the dose rate, the speed of the gantry, and the position of the MLC leaves can be adjusted dynamically. RapidArc and SmartArc are examples of VMAT. For most of the commercial planning solutions, no more than two arcs are needed to significantly improve the dose conformity. Rotating the MLC by 45° for VMAT can improve monitor unit efficiency [18].

Generally, VMAT deliver doses faster than IMRT, generating plans with higher or at least equivalent quality, with a very few exceptions. Due to necessary synchronization of both dose rate and gantry motion with MLC movement, it is clear that VMAT involves new and different QA steps relative to conventional IMRT. This should be reflected in acceptance testing (AT), commissioning (COM), and routine QA for VMAT. Finally, VMAT uses fewer monitor units resulting in lower patient total body dose. Plan quality is determined by the number of independent aperture variations generated by a conversion algorithm to produce the calcu‐ lated fluence maps. Specific controls should be used for this purpose [19].

Testing tools and Devices for VMAT Commissioning include dedicated phantoms, electronic portal imager or films, dedicated programmed MLC files (provided by vendors), and software for analysis. Testing protocols should be based on few parameters, defined method, and appropriate tolerance, supported by documentation or specific QA baselines.

In the Ling et al. paper based on a Varian accelerator for testing, proposed procedures were based on a good knowledge of the use of log files and relatively simple equipment.

In the Bedford et al. paper an Elekta accelerator was used for testing based on complex and expensive equipment [20, 21].

To validate VMAT, the understanding of the limits of planning optimization, gantry rotation, beam blocking, couch rotation, leaf speed, and collimator settings is a prerequisite.

Machine-specific QA should include the following:


The AAPM TG 142 report represents an update on the TG-40 report, specifying new tests and their tolerance, and added recommendations for not only the new ancillary delivery technol‐ ogies but also for imaging devices that are part of the linear accelerator. In particular, the imaging devices include X-ray imaging, photon portal imaging, and cone-beam CT.

Deviation from the baseline values could result in suboptimal treatment of patients. Machine parameters can deviate from their baseline values as a result of many reasons, such as unexpected changes in machine performance due to machine malfunctioning, mechanical breakdowns, physical accidents, or component failure. Major component replacement (waveguide, bending magnet, etc.) or degradation of components due to the aging of machines may also alter machine performance from the original parameters. These patterns of failure must be considered when establishing a periodic QA program.

Machines used for SRS/SBRT treatments, TBI, VMAT, or IMRT require different tests and/or tolerance. Specific tests could be adopted for dedicated machines such as tomotherapy, VERO, and Cyberknife. For these devices, vendors in some cases provide phantoms and software to be used, such as black box.

The patient-based QA for irradiation techniques involving spatially dishomogenous fluences needs 2D/3D arrays of dosimeters or matrixes (such as Mapcheck/Arccheck, seven-29/ Octavius, delta4, MatriXX/Compass, and Gafcromich), EPID-based dosimetric systems (EPIQA, dosimetry check, and DISO) and online systems attached to linac collimator (compass AP and DAVID). To be noted, a dosimetry check has been proposed as useful for tomotherapy, based on measurements from detectors integrated in the accelerators [22–26].

Additional dosimetric issues requiring novel devices/correction factors include the following: (1) small field dosimetry for which ongoing research suggests diamond-based detectors, microchambers, and scintillators; and (2) high-fluence irradiations chambers with appropriate correction factors, alanine, and Gafcromich [27–30].

#### **5. Use of scintillating fibers**

Scintillating fibers have been used extensively in experiments of high energy particles. They were used in detector tracers but primarily in calorimetric detectors to measure the corre‐

**Figure 1.** Scintillating fibers, glued in one ribbon, connected to the four arrays of photodiodes.

To validate VMAT, the understanding of the limits of planning optimization, gantry rotation,

**•** Ability of the system to vary accurately the dose rate and gantry speed during VMAT

The AAPM TG 142 report represents an update on the TG-40 report, specifying new tests and their tolerance, and added recommendations for not only the new ancillary delivery technol‐ ogies but also for imaging devices that are part of the linear accelerator. In particular, the

Deviation from the baseline values could result in suboptimal treatment of patients. Machine parameters can deviate from their baseline values as a result of many reasons, such as unexpected changes in machine performance due to machine malfunctioning, mechanical breakdowns, physical accidents, or component failure. Major component replacement (waveguide, bending magnet, etc.) or degradation of components due to the aging of machines may also alter machine performance from the original parameters. These patterns of failure

Machines used for SRS/SBRT treatments, TBI, VMAT, or IMRT require different tests and/or tolerance. Specific tests could be adopted for dedicated machines such as tomotherapy, VERO, and Cyberknife. For these devices, vendors in some cases provide phantoms and software to

The patient-based QA for irradiation techniques involving spatially dishomogenous fluences needs 2D/3D arrays of dosimeters or matrixes (such as Mapcheck/Arccheck, seven-29/ Octavius, delta4, MatriXX/Compass, and Gafcromich), EPID-based dosimetric systems (EPIQA, dosimetry check, and DISO) and online systems attached to linac collimator (compass AP and DAVID). To be noted, a dosimetry check has been proposed as useful for tomotherapy,

Additional dosimetric issues requiring novel devices/correction factors include the following: (1) small field dosimetry for which ongoing research suggests diamond-based detectors, microchambers, and scintillators; and (2) high-fluence irradiations chambers with appropriate

Scintillating fibers have been used extensively in experiments of high energy particles. They were used in detector tracers but primarily in calorimetric detectors to measure the corre‐

based on measurements from detectors integrated in the accelerators [22–26].

**•** Ability of the system to vary accurately the MLC leaf speed during VMAT delivery

imaging devices include X-ray imaging, photon portal imaging, and cone-beam CT.

beam blocking, couch rotation, leaf speed, and collimator settings is a prerequisite.

Machine-specific QA should include the following:

**•** Tolerances: baselines from commissioning.

delivery

156 Evolution of Ionizing Radiation Research

be used, such as black box.

**•** Accuracy of the MLC leaf positions during VMAT delivery

must be considered when establishing a periodic QA program.

correction factors, alanine, and Gafcromich [27–30].

**5. Use of scintillating fibers**

sponding features of hadronic particles and electromagnetic primaries. The measure of the energy absorbed and the topology of the shower were related to the properties of the incident particle. In recent years, scintillating fibers have been used to measure the density of energy absorbed in the fibers directly and hence the dose delivered by a beam of particles used in radiotherapy. Scintillating fibers have been used in some tests [31–34] in small volumes coupled to light guides for connection to the electronics of conversion and reading; in other tests, they were placed in a water phantom or water equivalent to guarantee an accurate measurement 3D [35–37].

Both the scintillating fibers and the light guides are subjected to the radiation beam in all the tests mentioned. The production of light for Cerenkov effect is negligible in the scintillating fibers compared to the scintillation light [38, 39]; it cannot be ignored in the light guides [40]. Systems with subtraction of this contribution were then required [40].

We experimented a different approach using scintillating fibers, performing tests of thera‐ peutic beams of electrons and photons. The detailed description of the material used and some results have been included in the papers [41–43]. In this chapter, we present the main issues raised and described in previous works and insert recent results obtained using the detector in a vertical configuration.

We used a homogeneous plane of scintillating fibers (380 BCF-60 square scintillating optical fibers produced by Saint Gobain Crystals, each fiber of 0.5 × 0.5 mm2 ) directly coupled to the conversion system and reading as shown in Fig. 1.

The fibers are square (0.5 mm per side) and glued in a single ribbon as shown in Fig. 1. To eliminate optical crosstalk among nearby fibers, each fiber is covered with a white EMA (Extra Mural Absorber).

The detector has been made using a ribbon of 20 × 20.5 cm2 but with a useful sensitive area of 17 × 20.5 cm2 because 3 cm of the fibers is covered of lead to shield the electronics.

The readout system is composed of photodiodes arranged along four arrays optically coupled with the fiber bundles.

We selected four arrays S8865-128 (Hamamatsu, Shizuoka, Japan), each with 128 photodiodes with a sensitive area of 0.3 × 0.6 mm2 and a pitch of 0.4 mm assembled as shown in Fig. 1, and four drivers C9118 (Hamamatsu) for the readout in sequence of the photodiodes.

The linear connection between the response in volts and the energy absorbed in the fibers is shown in [41].

The detector was tested using a 6-MV photon beam generated through a Varian Clinac 2100 DHX (Varian Medica Systems, Palo Alto, CA, USA) at the Cosenza Hospital (Cosenza, Italy).

The modalities used for the exposition were the same described by Lamanna et al. [43]. The integration time of 0.3 s was chosen to ensure a dynamic range large enough to have a linear response from the detector.

**Figure 2.** Detector response delivering the same dose to the fibers. The channels of the four arrays of photodiode are shown together with the electronic noise.

The response of the detector to the energy deposited in the scintillating fiber is determined by various contributions such as the production and the propagation of light in the fibers, the electronic gain, the coupling between the fibers and the photodiode array, and geometrical and optical. All these effects have been taken into account measuring a calibration factor for each photodiode response by exposing the fibers to the same dose, as explained in detail by Lamanna et al. [43]. We selected a beam of photons with field of view (FOV) 17 × 28 cm2 , large enough to cover half the size of the ribbon along the fiber axis.

The response of the detector is shown in Fig. 2. The choice of an integration time of 0.3 s ensures a dynamic range wide enough to have a voltage response in the linear region of the electronics readout. This region is limited between the response of the electronic noise and the saturation voltage. A weight for each channel was estimated to normalize the response of the photodio‐ des. All the measurements that follow were calibrated using Equation (1):

$$D\_i = W\_i \times \left(V\_i - N\_i\right) \text{ with } W\_i = \frac{1}{R\_i - N\_{R\_i}} \tag{1}$$

The index *i* is related to the *i*th photodiodes. *Di* is the relative calibrated response of the photodiode. *Wi* is the calibration factor (weight). *Vi* is the measure in volts. *Ni* is the electronic noise. *Ri* is the response when all the fibers are exposed to same dose (as shown in Fig. 2). *NRi* is the electronic noise associated with the response *Ri* .

**Figure 3.** Data taken in two different conditions, (a) red and (b) brown; the same data in blue and green after the cali‐ bration.

In Fig. 3, two distributions of data taken in different conditions and the same data after calibration are shown. The procedure described was used for the series of measurements that follow.

#### **6. Dose profile at fixed depth**

We selected four arrays S8865-128 (Hamamatsu, Shizuoka, Japan), each with 128 photodiodes with a sensitive area of 0.3 × 0.6 mm2 and a pitch of 0.4 mm assembled as shown in Fig. 1, and

The linear connection between the response in volts and the energy absorbed in the fibers is

The detector was tested using a 6-MV photon beam generated through a Varian Clinac 2100 DHX (Varian Medica Systems, Palo Alto, CA, USA) at the Cosenza Hospital (Cosenza, Italy).

The modalities used for the exposition were the same described by Lamanna et al. [43]. The integration time of 0.3 s was chosen to ensure a dynamic range large enough to have a linear

**Figure 2.** Detector response delivering the same dose to the fibers. The channels of the four arrays of photodiode are

The response of the detector to the energy deposited in the scintillating fiber is determined by various contributions such as the production and the propagation of light in the fibers, the electronic gain, the coupling between the fibers and the photodiode array, and geometrical and optical. All these effects have been taken into account measuring a calibration factor for each photodiode response by exposing the fibers to the same dose, as explained in detail by Lamanna et al. [43]. We selected a beam of photons with field of view (FOV) 17 × 28 cm2

The response of the detector is shown in Fig. 2. The choice of an integration time of 0.3 s ensures a dynamic range wide enough to have a voltage response in the linear region of the electronics readout. This region is limited between the response of the electronic noise and the saturation

enough to cover half the size of the ribbon along the fiber axis.

, large

four drivers C9118 (Hamamatsu) for the readout in sequence of the photodiodes.

shown in [41].

response from the detector.

158 Evolution of Ionizing Radiation Research

shown together with the electronic noise.

The dose profile at a fixed depth is reconstructed using an approach very similar to that adopted in X-ray computed tomography [38], reading 1D radon transformation of the dose absorbed.

**Figure 4.** Setup configuration for the horizontal exposition; the red area describes the beam field of view (FOV). The fiber ribbon is enclosed between two sheets of polystyrene to ensure the homogeneity top down.

The response of the detector was tested through exposure to a beam orthogonal to the ribbon surface as shown in Fig. 4. Two passive layers were inserted on the top and bottom of the fibers of thickness, respectively, of 1.6 and 5 cm. The polystyrene of density 1.05 g/cm3 , transparent to the light as the core of the fibers, was selected to build a homogeneous phantom.

**Figure 5.** Projected dose at 37 rotating angles around the beam axis. The data are normalized to the maximum value measured.

The field of view (FOV) of 8 × 8 cm2 was selected. The system was rotated manually around the beam axis, and the data were collected every 5° for a total of 36 positions from 5° to 180°. The distribution of doses, on the axis orthogonal to that of the fibers, is shown for each angle of rotation in Fig. 5. We observe a variation of the dose and of the width of the distributions, by varying the angle. Angles with maximum dose and minimum width are 45° and 135°, corresponding to a fiber orientation in the direction of the diagonals of rectangular FOV of the beam.

The 36 projections were used to reconstruct the transverse profile of the dose. Using a backprojection approach without filter, we obtained a poor profile, while the reconstruction, shown in Fig. 6, top left, seems to be more precise with the introduction of a ramp filter. A better reconstruction is obtained using the Hann filter, shown in Fig. 6, top right.

**Figure 4.** Setup configuration for the horizontal exposition; the red area describes the beam field of view (FOV). The

The response of the detector was tested through exposure to a beam orthogonal to the ribbon surface as shown in Fig. 4. Two passive layers were inserted on the top and bottom of the fibers

**Figure 5.** Projected dose at 37 rotating angles around the beam axis. The data are normalized to the maximum value

The field of view (FOV) of 8 × 8 cm2 was selected. The system was rotated manually around the beam axis, and the data were collected every 5° for a total of 36 positions from 5° to 180°. The distribution of doses, on the axis orthogonal to that of the fibers, is shown for each angle

measured.

160 Evolution of Ionizing Radiation Research

, transparent

fiber ribbon is enclosed between two sheets of polystyrene to ensure the homogeneity top down.

of thickness, respectively, of 1.6 and 5 cm. The polystyrene of density 1.05 g/cm3

to the light as the core of the fibers, was selected to build a homogeneous phantom.

**Figure 6.** Top: dose map reconstruction using a filtered back projection with ramp filter (left) and Hann filter (right). Bottom: comparison dose profile around *Y* = 0 measured using an ionization chamber superimposed on the recon‐ structed dose profiles using the back projection with and without filters.

A more accurate comparison is shown at the bottom of Fig. 6 where the reconstructed dose profiles, around the center of the beam, are superimposed on the profile obtained using the PTW Freiburg TM31010 ionization chamber. The reconstruction through the back projection approach with ramp or Hann filter, described in [44, 45], reproduces quite accurately the dose profile. A more detailed description of the method and some comments are provided by Lamanna et al. [43].

#### **7. Percentage depth dose**

The delivered dose in depth was measured by rotating the detector in a vertical exposition of the layer, as shown in Fig. 7.

**Figure 7.** Configuration of the detector for the vertical exposure.

The photon beam was delivered to the sensitive layer placed between two polystyrene sheets of 2.5 cm of thickness. An FOV of 6 × 6 cm2 was selected to contain the beam completely all along the fiber. In this configuration, the dose is measured along a line in the FOV area and a granularity of 0.5 mm in depth.

The percentage dose in depth (PDD) measured through the fiber detector (b) is superimposed on those obtained using the PTW TM31010 ionization chamber and the water phantom PTW MP3 (PTW, Freiburg, Germany) (a) in Fig. 8. The response of the fibers after the calibration is shown in curve c.

Two features emerge from the comparison of curves a and c:


The fiber response is in agreement with the ionization chamber after two corrections of the data. The first correction is reported in Equation (2):

$$\begin{aligned} \mathbf{PDD}\_i^d &= \mathbf{W}\_i^\star \mathbf{PDD}\_i^c \text{ with } \mathbf{W}\_i = \frac{\text{width}\_0}{\text{width}\_i} \\ \mathbf{width}\_0 &= \mathbf{6cm} \text{ :} \text{width}\_i = 0.08^\star \text{width}\_0 + \mathbf{6cm} \end{aligned} \tag{2}$$

**7. Percentage depth dose**

162 Evolution of Ionizing Radiation Research

the layer, as shown in Fig. 7.

**Figure 7.** Configuration of the detector for the vertical exposure.

Two features emerge from the comparison of curves a and c:

*d c ii i i*

data. The first correction is reported in Equation (2):

of 2.5 cm of thickness. An FOV of 6 × 6 cm2

granularity of 0.5 mm in depth.

**•** Shift of the point of maximum dose

**•** Different slopes of the curves

shown in curve c.

The delivered dose in depth was measured by rotating the detector in a vertical exposition of

The photon beam was delivered to the sensitive layer placed between two polystyrene sheets

along the fiber. In this configuration, the dose is measured along a line in the FOV area and a

The percentage dose in depth (PDD) measured through the fiber detector (b) is superimposed on those obtained using the PTW TM31010 ionization chamber and the water phantom PTW MP3 (PTW, Freiburg, Germany) (a) in Fig. 8. The response of the fibers after the calibration is

The fiber response is in agreement with the ionization chamber after two corrections of the

*i*

= =+

0 0

width 6 cm ; width 0.08\*width 6

*W W*

width PDD \* PDD with

= =

*i*

width

0

*cm*

(2)

was selected to contain the beam completely all

**Figure 8.** Percent dose depth (PDD) as a function of the depth. The blue curve (a) is the PDD measure through ioniza‐ tion chamber and water phantom at AO Cs; the black points (b) are the measured values in Volt; the brown points (c) are the (b) values, calibrated and normalized to the maximum value; the green points (d) are the (c) values corrected for width; the red points (e) are the (d) values after the correction of the depths.

**Figure 9.** Left side: dose profiles at different depths measured through the ionization chamber and a water phantom in the center of the FOV. Right side: full width at half maximum of the previous profiles as a function of the depth.

The integrated doses along each fiber are measured through the scintillating fibers, and the region of the absorbed dose increases in width as a function of the depths. The behavior is shown in the left region of Fig. 9, where the profiles of the dose at different depth in water for a 6-MV photon beam are plotted. The full width at half maximum of the profiles increases linearly with the depth, as shown on the right of Fig. 9.

The correction factor *Wi* guarantees the same integration length for all the fibers at different depths. The results are shown in curve d of Fig. 8. The slope is close to that of the curve obtained through the ionization chamber but they are not equal.

The second correction is reported in Equation (3):

$$\mathbf{Depth}\_{i}^{\text{H}\_{2}\text{O}} = I\mathbf{W}\_{i} \times \mathbf{Depth}\_{i}^{\text{C}\_{8}\text{H}\_{8}} \text{ with } I\mathbf{W}\_{i} = \frac{\text{ionization} \left(\text{H}\_{2}\text{O}\right)\_{i}}{\text{ionization} \left(\text{C}\_{8}\text{H}\_{8}\right)\_{i}} \tag{3}$$

In the assembled configuration to measure the PDD, shown in Fig. 7, both the layer of scintillating fibers and the passive sheets are mainly made up of transparent polystyrene (C8H8). The ionization is different from that in the water at the same depth. The correction factor *IWi* is needed to find the depth in water corresponding to the ionization measured in polystyrene.

The factor *IW* has been measured by exposing two phantoms, a water and a transparent polystyrene phantom, in the same conditions. We used a beam of electrons of 9 MeV. The results are shown in Fig. 10. The two behaviors are different. The correction factor in depth IW has been evaluated to produce a full superposition.

**Figure 10.** Dose measured through the ionization chamber, in water (black) and in a phantom of transparent polystyr‐ ene (red), at different depths. A correction factor for the depth has been evaluated to superimpose the two sets of data. The green points are the red points with the correction of the depths using Equation (3).

The layer of scintillating fibers can be used to measure the PDD in a vertical configuration of the exposure, taking into account that the integration of the dose along the fiber requires the corrections inserted in Equations (2) and (3).

#### **8. Conclusions**

The correction factor *Wi*

164 Evolution of Ionizing Radiation Research

polystyrene.

through the ionization chamber but they are not equal.

*ii i i*

The second correction is reported in Equation (3):

has been evaluated to produce a full superposition.

guarantees the same integration length for all the fibers at different

( ) ( ) *i*

ionization H O

Depth Depth with ionization C H = ´ <sup>=</sup> (3)

8 8

*i*

depths. The results are shown in curve d of Fig. 8. The slope is close to that of the curve obtained

<sup>2</sup> *IW* 8 8 *IW* H O C H <sup>2</sup>

In the assembled configuration to measure the PDD, shown in Fig. 7, both the layer of scintillating fibers and the passive sheets are mainly made up of transparent polystyrene (C8H8). The ionization is different from that in the water at the same depth. The correction factor *IWi* is needed to find the depth in water corresponding to the ionization measured in

The factor *IW* has been measured by exposing two phantoms, a water and a transparent polystyrene phantom, in the same conditions. We used a beam of electrons of 9 MeV. The results are shown in Fig. 10. The two behaviors are different. The correction factor in depth IW

**Figure 10.** Dose measured through the ionization chamber, in water (black) and in a phantom of transparent polystyr‐ ene (red), at different depths. A correction factor for the depth has been evaluated to superimpose the two sets of data.

The layer of scintillating fibers can be used to measure the PDD in a vertical configuration of the exposure, taking into account that the integration of the dose along the fiber requires the

The green points are the red points with the correction of the depths using Equation (3).

corrections inserted in Equations (2) and (3).

The new techniques of delivering the therapeutic dose to the tumor tissues with an external beam require dosimeters that have better spatial and time resolutions than the standard detectors used in current clinical practice. The properties of scintillating fibers of dimensions less than 1 mm and their gluing in homogeneous layers allow these requirements to be obtained. The single-layer 1D can be used to reconstruct the dose profiles XY at a fixed depth, adopting the tomographic technique of filtered back-projection. The same configuration 1D may be used to measure the dose profiles in depth by applying the corrections inserted in Equations (2) and (3).

The final response is quite rapid. The data are acquired in few milliseconds and processed in 2–3 s, using a single layer. This characteristic together with the reduced thickness of two orthogonal layers in a 2D configuration (1 mm of water equivalent), allow the use of layers of fibers also online to measure the characteristics of an incident beam (a similar approach was published in [46]).

The positive results obtained and described in this chapter justify an investment of this approach and suggest some directions for future developments:


#### **Nomenclature**

AAPM; American Association of Physicists in Medicine

AT ; acceptance testing

COM ; commissioning

EBR; external beam radiotherapy

EBTR; evidence-based timeline retrospective

FOV; field of view

FPD; flat panel detector

IMRT; intensity-modulated radiation therapy

MLC; multileaf collimator MPPC; multipixel photon counters PDD; percentage depth dose QA; quality assurance SRS; stereotactic radiosurgery RT; radiotherapy TBI; traumatic brain injury UM; monitor units VMAT; volumetric-modulated arc therapy

#### **Acknowledgements**

We are grateful to the Italian INFN (National Institute of Nuclear Physics) for supporting the study of scintillating fiber dosimeters and the "Hospital of Cosenza" for allowing the use of the accelerator Varian to test the dosimeter.

#### **Author details**

Ernesto Lamanna1\*, Bianco Cataldo2 , Giulia Marvaso2 , Marco D'Andrea3 and Lidia Strigari3

\*Address all correspondence to: lamanna@unicz.it

1 Department of Health Sciences, Magna Graecia University, Catanzaro, Italy

2 Department of Experimental and Clinical Medicine, Magna Graecia University, Catanzaro, Italy

3 Department of Medical Physics, Istituto Regina Elena, Roma, Italy

#### **References**

[1] Raju MR. Particle radiotherapy: historical developments and current status. Radiat Res 1996; 145, 391–407.

[2] Slater JM. From X-rays to ion beams: a short history of radiation therapy. In: U. Linz. (Ed.), Ion Beam Therapy. Biological and Medical Physics, Biomedical Engineering. Berlin: Springer-Verlag, 2012. DOI: 10.1007/978-3-642-21414-1 1.

MLC; multileaf collimator

166 Evolution of Ionizing Radiation Research

PDD; percentage depth dose

SRS; stereotactic radiosurgery

TBI; traumatic brain injury

**Acknowledgements**

**Author details**

Italy

**References**

VMAT; volumetric-modulated arc therapy

the accelerator Varian to test the dosimeter.

\*Address all correspondence to: lamanna@unicz.it

Ernesto Lamanna1\*, Bianco Cataldo2

Res 1996; 145, 391–407.

We are grateful to the Italian INFN (National Institute of Nuclear Physics) for supporting the study of scintillating fiber dosimeters and the "Hospital of Cosenza" for allowing the use of

, Giulia Marvaso2

2 Department of Experimental and Clinical Medicine, Magna Graecia University, Catanzaro,

[1] Raju MR. Particle radiotherapy: historical developments and current status. Radiat

1 Department of Health Sciences, Magna Graecia University, Catanzaro, Italy

3 Department of Medical Physics, Istituto Regina Elena, Roma, Italy

, Marco D'Andrea3

and Lidia Strigari3

QA; quality assurance

RT; radiotherapy

UM; monitor units

MPPC; multipixel photon counters


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[16] Salama JK, Kirkpatrick JP, Yin FF. Stereotactic body radiotherapy treatment of extrac‐

[17] Ezzell GA, Burmeister JW, Dogan N, et al. IMRT commissioning: multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119. Med

[18] Yu CX. Intensity-modulated arc therapy with dynamic multileaf collimation: an al‐

[19] Phillips MH, Holdsworth C. When is better best? A multi-objective perspective. Med

[20] Ling C, et al. Commissioning and quality assurance of RapidArc radiotherapy deliv‐

[21] Bedford JL, Warrington AP. Commissioning of volumetric modulated arc therapy.

[22] Hussein M1, Rowshanfarzad P, Ebert MA, Nisbet A, Clark CH. A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems. Radiother

[23] Watanabe Y, Nakaguchi Y. 3D evaluation of 3DVH program using BANG3 polymer

[24] Nakaguchi Y, Araki F, Ono T, Tomiyama Y, Maruyama M, Nagasue N, Shimohigashi Y, Kai Y. Validation of a quick three-dimensional dose verification system for pre-

[25] Fredh A, Scherman JB, Fog LS, Munck af Rosenschöld P. Patient QA systems for ro‐ tational radiation therapy: a comparative experimental study with intentional errors.

[26] Cilla S, Azario L, Greco F, Fidanzio A, Porcelli A, Grusio M, Macchia G, Morganti AG, Meluccio D, Piermattei A. An in-vivo dosimetry procedure for Elekta step and

[27] Marsolat F, Tromson D, Tranchant N, Pomorski M, Le Roy M, Donois M, Moignau F, Ostrowsky A, De Carlan L, Bassinet C, Huet C, Derreumaux S, Chea M, Cristina K, Boisserie G, Bergonzo P. A new single crystal diamond dosimeter for small beam: comparison with different commercial active detectors. Phys Med Biol 2013 Nov

[28] Di Venanzio C, Marinelli M, Milani E, Prestopino G, Verona C, Verona-Rinati G, Fal‐ co MD, Bagalà P, Santoni R, Pimpinella M. Characterization of a synthetic single crystal diamond Schottky diode for radiotherapy electron beam dosimetry. Med

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168 Evolution of Ionizing Radiation Research


#### **Chapter 7**

## **Linac Twins in Radiotherapy**

Marius Treutwein, Petra M. Härtl, Christian Gröger, Zaira Katsilieri and Barbara Dobler

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60427

#### **Abstract**

[41] Lamanna E, Fiorillo AS, Bruno C, Santaniello A, Siaka YFT, Berdondini A, Bettuzzi M, Brancaccio R, Casali F, Morigi MP, Barca G, Castrovillari F. Dosimetry of high in‐ tensity electron beams produced by dedicated accelerators in intra-operative radia‐

[42] Lamanna E, Fiorillo AS, Gallo A, Trapasso A, Caroleo R, Brancaccio R, Barca G, Car‐ nevale S, Castrovillari F, Tchuente Siaka YF. Dosimetric study of therapeutic beams using a homogeneous scintillating fiber layer. Nuclear Science Symposium and Med‐ ical Imaging Conference (NSS/MIC), 2011 IEEE, pp. 244–248, 23–29 Oct. 2011. ISBN:

[43] Lamanna E, Fiorillo AS, Gallo A, Trapasso A, Caroleo R, Brancaccio R, Barca G, Car‐ nevale S, Castrovillari F, Tchuente Siaka YF. Dosimetric study of therapeutic beams using a homogeneous scintillating fiber layer. IEEE Trans Nucl Sci 2013;60 (1):109–14.

[44] Quinto ET. Tomographic reconstructions from incomplete data-numerical inversion

[45] Lyra M, Ploussi A. Filtering in SPECT image reconstruction. Int J Biomed Imaging

[46] Goulet M, Gingras L, Beaulieu L. Real-time verification of multileaf collimator-driven radiotherapy using a novel optical attenuation-based fluence monitor. Med Phys

of the exterior Radon transform. Inverse Problems 1988;4 (3):867.

tion therapy (IORT). IEEE Trans Nucl Sci 2009;56 (1):66–72.

978-1-4673-0119-0.

170 Evolution of Ionizing Radiation Research

2011; ID 693795.

2011;38:1459–1459.

In a radiotherapy department having more than one linear accelerator, it is rather common to match the dose output of all machines. In particular, the recently developed flattening filter free mode requires new investigations regarding the feasibility of matching and the consequences for quality assurance and workload. This refers also to the beam model of the radiotherapy treatment planning system. Our results show that matching is possible not only for flat beams but also for flattening filter free mode. Therefore, the machines can substitute each other in the case of breakdown or service without new treatment planning even in the case of complex intensity-modulated radiotherapy or volumetric-modulated arc therapy. The quality assurance is reduced to only one data set for both the linear accelerators and the radiotherapy treatment planning system.

**Keywords:** linac twins, matched linacs, flatness filter free, FFF, quality assurance

#### **1. Introduction**

Electron linear accelerators (linacs) are the most common treatment machines in radiotherapy. Having two (or more) equal linacs (*linac twins* or also called *matched linacs*) enables a radio‐ therapy department to facilitate the workflow and to reduce the amount of quality assurance. The major part of the German standards (DIN) regarding quality assurance of medical linear accelerators has been reworked or has been published for the first time in the recent years due to technical developments. Similar updates have been published in other countries, e.g., by

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

different task groups of the American Association of Physicists in Medicine (AAPM) [1-3]. However, these updates have again been overtaken by a technical novelty: the flattening filter free (FFF) mode. In modern linacs, it allows higher dose rates than used in the standard mode with flattening filter (up to three or four times), thus reducing treatment times at the cost of a nonflattened profile. This mode requires its own procedures for acceptance and quality assurance [4, 5].

The aims of this study are to setup a commissioning procedure and a quality assurance program for linac twins and to investigate if the time required for commissioning and quality assurance can be reduced as compared to two linacs of different types. This includes also the radiotherapy treatment planning system (RTPS). Although this investigation refers to the German standards and directives, the principles are valid for all countries. Although the concept of matched linacs has been mentioned earlier [6-10], the consequences for the quality assurance and standardization have not yet been regarded. This study will only investigate photon beam qualities. Characteristics of electron beams, portal imaging systems, and cone beam CT are not included. Although the concept and first results have been part of a congress proceeding [11], this chapter presents for the first time elaborated and generalized background, results, and discussion.

#### **2. Materials and methods**

#### **2.1. Linacs**

Tenders were invited to provide two linacs of the same type to replace the old Siemens Primus machines. We asked for linacs with two photon energies (6 and 15 MV) flattened beams (FB), additional FFF option for 6 MV, capability of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), and five to six different electron energies between 4 and 22 MeV. Our requirement was that patients should be treatable at both machines with the same treatment plan. The first of the twin machines (Figure 1), an Elekta Synergy™ with Agility head, XVI cone beam CT, and Iview GT™ portal imaging, has been installed and commissioned according to earlier experiences [12] and has been running in the clinical routine for several months, but initially not FFF. The desktop software is Integrity 3.1. For the second linac, the installation has been completed in June 2014. The manufacturer specifies a routine for acceptance testing of linear accelerators [13], which refers to matched machines only pertaining to the beam quality.

#### **2.2. Standards and guidelines for quality assurance**

Although commissioning tests, the determination of basic performance characteristics, and consistency tests for linacs according the German standards [20] have to be accomplished for each machine, they can at least be set up identically without modifications for twin machines. This is also applicable for performance characteristics and consistency testing concerning special techniques as stereotactic radiotherapy [15, 16] and IMRT [17, 18], as well as electronic portal imaging devices (EPID) [14].

systems, and cone beam CT are not included. Although the concept and first results have been part of a congress proceeding [11], this chapter presents for the first time elaborated

Tenders were invited to provide two linacs of the same type to replace the old Siemens Primus machines. We asked for linacs with two photon energies (6 and 15 MV) flattened beams (FB), additional FFF option for 6 MV, capability of intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc therapy (VMAT), and five to six different electron energies between 4 and 22 MeV. Our requirement was that patients should be treatable at both machines with the same treatment plan. The first of the twin machines (Figure 1), an Elekta Synergy™ with Agility head, XVI cone beam CT, and Iview GT™ portal imaging, has been installed and commissioned according to earlier experiences [12] and has been running in the clinical routine for several months, but initially not FFF. The desktop software

and generalized background, results, and discussion.

**2. Materials and methods** 

*2.1. Linacs* 

**Figure 1.** Figure 1. First and second of the linac First and second of the linac twins: Elekta Synergy with Agility head. twins: Elekta Synergy with Agility head.

The draft of the German standard for consistency tests of RTPS DIN 6873-5 [20] requires calculations for each treatment machine. Probably part 1 of DIN 6873 for commissioning of RTPS which is in development will demand this too. A technical report of the Interna‐ tional Atomic Energy Agency (IAEA) [21] recommends checks for each photon and electron beam used in clinical planning and therefore each beam model and treatment machine. Having only one treatment machine model reduces time and effort for quality assurance and commissioning.

#### **2.3. RTPS and water phantom**

different task groups of the American Association of Physicists in Medicine (AAPM) [1-3]. However, these updates have again been overtaken by a technical novelty: the flattening filter free (FFF) mode. In modern linacs, it allows higher dose rates than used in the standard mode with flattening filter (up to three or four times), thus reducing treatment times at the cost of a nonflattened profile. This mode requires its own procedures for acceptance and quality

The aims of this study are to setup a commissioning procedure and a quality assurance program for linac twins and to investigate if the time required for commissioning and quality assurance can be reduced as compared to two linacs of different types. This includes also the radiotherapy treatment planning system (RTPS). Although this investigation refers to the German standards and directives, the principles are valid for all countries. Although the concept of matched linacs has been mentioned earlier [6-10], the consequences for the quality assurance and standardization have not yet been regarded. This study will only investigate photon beam qualities. Characteristics of electron beams, portal imaging systems, and cone beam CT are not included. Although the concept and first results have been part of a congress proceeding [11], this chapter presents for the first time elaborated and generalized background,

Tenders were invited to provide two linacs of the same type to replace the old Siemens Primus machines. We asked for linacs with two photon energies (6 and 15 MV) flattened beams (FB), additional FFF option for 6 MV, capability of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), and five to six different electron energies between 4 and 22 MeV. Our requirement was that patients should be treatable at both machines with the same treatment plan. The first of the twin machines (Figure 1), an Elekta Synergy™ with Agility head, XVI cone beam CT, and Iview GT™ portal imaging, has been installed and commissioned according to earlier experiences [12] and has been running in the clinical routine for several months, but initially not FFF. The desktop software is Integrity 3.1. For the second linac, the installation has been completed in June 2014. The manufacturer specifies a routine for acceptance testing of linear accelerators [13], which refers to matched machines only

Although commissioning tests, the determination of basic performance characteristics, and consistency tests for linacs according the German standards [20] have to be accomplished for each machine, they can at least be set up identically without modifications for twin machines. This is also applicable for performance characteristics and consistency testing concerning special techniques as stereotactic radiotherapy [15, 16] and IMRT [17, 18], as well as electronic

assurance [4, 5].

172 Evolution of Ionizing Radiation Research

results, and discussion.

**2.1. Linacs**

**2. Materials and methods**

pertaining to the beam quality.

portal imaging devices (EPID) [14].

**2.2. Standards and guidelines for quality assurance**

For commissioning of the linac model in the RTPS Oncentra® 4.3 (by Nucletron an Elekta Company), a set of geometrical data, absolute, and relative dose measurements have been measured [22] using a water phantom of the type Blue Phantom² of IBA company. It has been operated by the software OmniPro Accept 7.4, including a module for data export for Oncen‐ tra®. The data are processed by Elekta to create a model of the treatment unit, which takes several weeks according to our experience. Once the model is delivered by the company, it has to be validated by the customer. The RTPS comprises for this purpose the Beam Data Tool, which allows not only to compare measured and calculated dose distributions but also to adapt the size of the focus and the transmission of the collimator for final optimization. One aim of the study is to investigate if this procedure can be reduced to the validation process for the second linac.

The evaluation tools of the water phantom software were used to compare the measured dose distributions of both machines. For the graphical demonstrations, smoothing with least square algorithms was performed to get rid of some noise, and the curves were renormalized to the dose maximum on the central beam. The Beam Data Tool of the RTPS was applied for comparisons of measured and calculated dose distributions. For the calculations, the collapsed cone algorithm was used. The European Society for Radiotherapy and Oncology (ESTRO) gives tolerances as confidence limits for calculated doses [23]. The specifications of the manufacturer of the RTPS Oncentra® [24] are not always comparable, e.g., the shoulder region is not defined exactly, or dose deviations refer to different points, or different units are used (Table 1). We referred to the manufacturer's specifications in our evaluations as they have to be kept by the manufacturer's beam model and used the ESTRO's—modified to a gamma evaluation of 10% and 2 mm in the sharp gradient area—only for further investigations. Distance to agreement, dose deviation, and gamma evaluation [25] are the integrated evalua‐ tion options in the Beam Data Tool. The depth dose distributions and profiles in in-plane and cross-plane direction in depths of 5, 10, and 20 cm were evaluated for square field sizes of 2, 5, 10, 15, 20, 30, and 40 cm.

From the measured depth dose curves of fields of 10 × 10 cm² at a source surface distance (SSD) of 100 cm, the beam quality was derived as *Q* = D200/D100, with D200 the dose in 20 cm depth and D100 in 10 cm.


**Table 1.** Accuracy of dose calculations in percent of calibration dose or mm distance deviation to correct dose value

#### **2.4. Breakdown concept**

The German directive "Strahlenschutz in der Medizin" [26], paragraph 2.3.4, requires a concept to ensure patient treatment even during machine down times (e.g., maintenance or break‐ down). Linac twins allow shifting all patients from one machine to the other without calcu‐ lating new treatment plans. Sjöström et al. [8] provided this as main argument for matching linacs. Depending on the tumor type and the patient state, such a transfer is also advised by the Board of Faculty of Clinical Oncology of the Royal College of Radiologists [27].

The record and verify system (Mosaiq®, version 2.50) can be configured in a manner that fields for one machine can be delivered at the other without warnings or password confirmation. Some VMAT and IMRT plans (FB and FFF) calculated with the beam model for the first machine were measured on the other to verify the exchangeability using the 2D array Matrixx Evolution phantom and software OmniPro-I'mRT, version 1.7 of IBA.

The procedure for these plan verifications has been described in detail in earlier publications [12, 28]. The patient plans were transferred to a cuboid phantom of solid water (RW3 of the PTW company) with the Matrixx phantom in the center in a horizontal plane. The dose distribution was recalculated without modification of any parameter. When the phantom was irradiated with the original plan, the software recorded the dose. The measured dose was compared to the calculated dose by gamma evaluation [25] with a dose tolerance of 3% of the maximum dose and a distance to agreement of 3 mm. The first clinical IMRT plans with 6MV and for testing of the feasibility some single IMRT plans with 6MV FFF and VMAT plans were evaluated.

#### **3. Results**

The evaluation tools of the water phantom software were used to compare the measured dose distributions of both machines. For the graphical demonstrations, smoothing with least square algorithms was performed to get rid of some noise, and the curves were renormalized to the dose maximum on the central beam. The Beam Data Tool of the RTPS was applied for comparisons of measured and calculated dose distributions. For the calculations, the collapsed cone algorithm was used. The European Society for Radiotherapy and Oncology (ESTRO) gives tolerances as confidence limits for calculated doses [23]. The specifications of the manufacturer of the RTPS Oncentra® [24] are not always comparable, e.g., the shoulder region is not defined exactly, or dose deviations refer to different points, or different units are used (Table 1). We referred to the manufacturer's specifications in our evaluations as they have to be kept by the manufacturer's beam model and used the ESTRO's—modified to a gamma evaluation of 10% and 2 mm in the sharp gradient area—only for further investigations. Distance to agreement, dose deviation, and gamma evaluation [25] are the integrated evalua‐ tion options in the Beam Data Tool. The depth dose distributions and profiles in in-plane and cross-plane direction in depths of 5, 10, and 20 cm were evaluated for square field sizes of 2,

From the measured depth dose curves of fields of 10 × 10 cm² at a source surface distance (SSD) of 100 cm, the beam quality was derived as *Q* = D200/D100, with D200 the dose in 20 cm depth

**Table 1.** Accuracy of dose calculations in percent of calibration dose or mm distance deviation to correct dose value

The German directive "Strahlenschutz in der Medizin" [26], paragraph 2.3.4, requires a concept to ensure patient treatment even during machine down times (e.g., maintenance or break‐ down). Linac twins allow shifting all patients from one machine to the other without calcu‐ lating new treatment plans. Sjöström et al. [8] provided this as main argument for matching linacs. Depending on the tumor type and the patient state, such a transfer is also advised by

The record and verify system (Mosaiq®, version 2.50) can be configured in a manner that fields for one machine can be delivered at the other without warnings or password confirmation. Some VMAT and IMRT plans (FB and FFF) calculated with the beam model for the first machine were measured on the other to verify the exchangeability using the 2D array Matrixx

the Board of Faculty of Clinical Oncology of the Royal College of Radiologists [27].

Evolution phantom and software OmniPro-I'mRT, version 1.7 of IBA.

Central 80% of field ±3% ±3% Shoulder region ±4% ±2 mm Regions outside the field ±5% ±30% local dose Regions of sharp gradient ±3 mm ±2 mm or 10%

**Specifications Oncentra® Recommendations ESTRO**

5, 10, 15, 20, 30, and 40 cm.

174 Evolution of Ionizing Radiation Research

and D100 in 10 cm.

**2.4. Breakdown concept**

#### **3.1. Beam quality and measured dose distributions**

The results of the beam quality evaluation of the percentage depth dose curves are given in Table 2.


**Table 2.** Beam quality *Q* = D200/D100 for both machines at the three photon beam qualities.

Although these nearly identical values have been calculated only for field size 10 × 10 cm², the depth dose curves in Figures 2, 3, and 4 show that the beam quality is comparable with other field sizes too as it is derived from depth dose parameters. Most of the curves are congruent. The presented figures show only a selection of all measured photon depth dose distributions. Due to the high congruence, the colors are often not clearly defined as in the figure texts.


**Table 3.** Evaluation of the field size of 6 MV photons in cross-plane direction as given by the profiles in Figure 5.

**Figure 2.** Depth dose curves for both machines of 6MV photons for square fields of 2, 10, 15, and 20 cm (left to right in the descending part). Red colors belong to the first, blue to the second linac.

**Figure 3.** Depth dose curves for both machines of 6MV photons FFF for square fields of 2, 10, 15, and 20 cm (left to right in the descending part). Red colors belong to the first, blue to the second linac.

**Figure 4.** Depth dose curves for both machines of 15MV photons for square fields of 2, 10, 15, and 20 cm (left to right in the descending part). Red colors belong to the first, blue to the second linac.

**Figure 2.** Depth dose curves for both machines of 6MV photons for square fields of 2, 10, 15, and 20 cm (left to right in

**Figure 3.** Depth dose curves for both machines of 6MV photons FFF for square fields of 2, 10, 15, and 20 cm (left to

right in the descending part). Red colors belong to the first, blue to the second linac.

the descending part). Red colors belong to the first, blue to the second linac.

176 Evolution of Ionizing Radiation Research

The second group of figures shows profiles in the cross-plane direction in a depth of 10 cm. Others with further field sizes, in different depths, and in in-plane direction have been measured with similar results. The difference between the flattened and the flatness filter free mode is obvious; as the angular distribution of the bremsstrahlung is not compensated, the maximum dose is always on the central beam. The high congruence of the corresponding curves makes often only one of them visible, sometimes in a mixed color. Numerical values of the field size evaluation are given in Table 3.

**Figure 5.** Profiles for both machines of 6MV photons for square fields of 2, 5, 10, 15, and 20 cm. Red colors belong to the first, blue to the second linac.

**Figure 6.** Profiles for both machines of 6MV FFF photons for square fields of 2, 5, 10, 15, and 20 cm. Red colors belong to the first, blue to the second linac.

**Figure 7.** Profiles for both machines of 15MV photons for square fields of 2, 5, 10, 15, and 20 cm. Red colors belong to the first, blue to the second linac.

#### **3.2. RTPS commissioning**

As described above, no model for the second linac has been created in the RTPS, but all calculations were done with the first linac model and compared to the measurements of the second. Figure 8 shows the results of such a validation at an example of FFF profiles. The left ordinate refers to the measured and calculated profiles (green and orange), the right to the validation criterion. In the first step, both curves are compared using the dose deviation of the calculated dose from the measured dose. The horizontal orange lines show the limits of ±3%. They are not valid in the region of the field borders (high gradient). Therefore, the evaluation was repeated plotting the distance to the next point with the same dose with a distance to agreement of 3 mm in the second step. Here all points in this region are within the limits. second. Figure 8 shows the results of such a validation at an example of FFF profiles. The left ordinate refers to the measured and calculated profiles (green and orange), the right to the validation criterion. In the first step, both curves are compared using the dose deviation of the calculated dose from the measured dose. The horizontal orange lines show the limits of ±3%. They are not valid in the region of the field borders (high gradient). Therefore, the evaluation was repeated plotting the distance to the next point with the same dose with a distance to agreement of 3 mm in the second step. Here all points in this region are within

calculations were done with the first linac model and compared to the measurements of the

*3.2. RTPS commissioning* 

the limits.

**Figure 6.** Profiles for both machines of 6MV FFF photons for square fields of 2, 5, 10, 15, and 20 cm. Red colors belong

**Figure 7.** Profiles for both machines of 15MV photons for square fields of 2, 5, 10, 15, and 20 cm. Red colors belong to

As described above, no model for the second linac has been created in the RTPS, but all calculations were done with the first linac model and compared to the measurements of the second. Figure 8 shows the results of such a validation at an example of FFF profiles. The left

to the first, blue to the second linac.

178 Evolution of Ionizing Radiation Research

the first, blue to the second linac.

**3.2. RTPS commissioning**

Figure 8. Profiles 6MV FFF as examples of the validation of the first linac model (calculated profiles in orange) in the RTPS for the second linac (measurements in green). In the upper part, a dose evaluation is shown (also in orange) referring to the right ordinate, in the lower part a distance to agreement **Figure 8.** Profiles 6MV FFF as examples of the validation of the first linac model (calculated profiles in orange) in the RTPS for the second linac (measurements in green). In the upper part, a dose evaluation is shown (also in orange) re‐ ferring to the right ordinate, in the lower part a distance to agreement evaluation.

evaluation. All depth doses for 6MV, 15MV, and 6MV FFF were within the tolerances given by the specifications of the manufacturer. One example is shown in Figure 9. For a total amount of 42 analyzed profiles per energy, the specifications were met in the central region in every case. They were only excessed in single points in the gradient region of 6 MV for the smallest field size (2 cm square). The ESTRO recommendations were failed in single points of the two largest field sizes for the sharp gradient regions.

**Figure 9.** Depth dose curves of 6MV photons (calculation in red, measurement in green) for a field size of 2 cm square. The dose difference curve (also in red) refers to the right ordinate.

#### **3.3. IMRT and VMAT plan verifications**

Figures 10 and 11 show the evaluations of a VMAT plan with 6 MV and of an IMRT plan with 6MV FFF as it is presented on the screen of the OmniPro-I'mRT software. The upper left corner demonstrates the calculated dose distribution in the measurement plane, below the measured dose distribution can be seen. The upper-right corner presents profiles in both planes (calcu‐ lated in red, measured in green). The position and the direction of these profiles are variable. The lower-right corner shows the gamma evaluation. Pixels in blue and white passed the evaluation. The number of pixels representing a specified value is given in the histogram below. Plans with a passing rate of 95% or more are accepted.

#### **4. Discussion**

The conformity of the depth dose distributions for the linac twins could be shown in the beam quality and the depth dose curves. The differences are in the order of repeated measurements at the same device. The quite unchanged beam quality of 6MV and 6MV FFF shows that not only the linacs are matched but also the FFF mode is matched to the flattened mode [29]. This is not self-evident; the beam hardening of the flattening filter must be compensated by the energy selection [30] that has been performed by the manufacturer.

The slight difference in the field size for the larger fields is within the specifications of the manufacturer [13]. However, this could be adjusted by the service engineer. From a practical point of view, the measured dose distributions are equivalent.

Therefore, the results allowed to continue with the validation of the model of the first machine in the RTPS for the employment at the second one. Deviations from the calculated dose above

**Figure 9.** Depth dose curves of 6MV photons (calculation in red, measurement in green) for a field size of 2 cm square.

Figures 10 and 11 show the evaluations of a VMAT plan with 6 MV and of an IMRT plan with 6MV FFF as it is presented on the screen of the OmniPro-I'mRT software. The upper left corner demonstrates the calculated dose distribution in the measurement plane, below the measured dose distribution can be seen. The upper-right corner presents profiles in both planes (calcu‐ lated in red, measured in green). The position and the direction of these profiles are variable. The lower-right corner shows the gamma evaluation. Pixels in blue and white passed the evaluation. The number of pixels representing a specified value is given in the histogram

The conformity of the depth dose distributions for the linac twins could be shown in the beam quality and the depth dose curves. The differences are in the order of repeated measurements at the same device. The quite unchanged beam quality of 6MV and 6MV FFF shows that not only the linacs are matched but also the FFF mode is matched to the flattened mode [29]. This is not self-evident; the beam hardening of the flattening filter must be compensated by the

The slight difference in the field size for the larger fields is within the specifications of the manufacturer [13]. However, this could be adjusted by the service engineer. From a practical

Therefore, the results allowed to continue with the validation of the model of the first machine in the RTPS for the employment at the second one. Deviations from the calculated dose above

The dose difference curve (also in red) refers to the right ordinate.

below. Plans with a passing rate of 95% or more are accepted.

energy selection [30] that has been performed by the manufacturer.

point of view, the measured dose distributions are equivalent.

**3.3. IMRT and VMAT plan verifications**

180 Evolution of Ionizing Radiation Research

**4. Discussion**

Figure 10. Plan verification of a VMAT plan with 6MV calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 99%, which **Figure 10.** Plan verification of a VMAT plan with 6MV calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 99%, which is indicated in the histogram below.

the specifications are exceptions in single points and have been assessed clinically to be acceptable. For example, exceeding the gamma criterion of 10% and 2 mm for the largest field size in the sharp gradient area can be traced back to the slightly different field size calibration is indicated in the histogram below.

Figure 11. Plan verification of an IMRT plan with 6MV FFF, calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 97% which is indicated in the histogram below. **Figure 11.** Plan verification of an IMRT plan with 6MV FFF, calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 97% which is indicated in the histogram below.

of both machines, which has also be seen in the comparison of the measure data. Nevertheless, the specification of the manufacturer with a distance to agreement of 3 mm was met.

Thus, the compatibility of the linac twins has been proven for the depth dose distributions and profiles on both main axes in different depths and for the full range of collimator apertures. The acceptance test of the manufacturer for matched linacs, which only refers to the beam quality, is only a first step and runs too short as it has also been reported for the matching process of another manufacturer [8].

The evaluations of different IMRT and VMAT plans, which had been calculated for the first machine and irradiated at the second one, showed very good results. The passing rates were in the same range as they had been seen for verifications at the "original" machine. The beam model in the RTPS of the first machine has been demonstrated sufficient for the second machine even for plans of very high complexity as IMRT with 6MV FFF or VMAT. This means that the second linac can substitute the first one in cases of breakdown. Chang et al. [10] had similar satisfying results for three matched Varian linacs. However, they first measured the data of all three linacs and combined them by averaging to get composite beam data. Having a time interval of several months or more between the installation of different linacs, as it is given in the case of replacement of old machines, this procedure is not applicable.

#### **5. Conclusion**

It has been shown that the dose distributions for all photon energies and modes could be adjusted equivalent. The new FFF mode presents no exceptions. Plan verifications of complex IMRT and VMAT plans demonstrate the exchangeability of the linacs also for the FFF mode, allowing continued therapy during downtimes, e.g., service works. Our results confirm that the time and effort for commissioning and quality assurance can be reduced for linac twins:


#### **Nomenclature**

DIN; Deutsches Institut für Normung (German Institute for Standards)

ESTRO; European Society for Radiotherapy and Oncology

FFF; Flattening filter free

IMRT ; Intensity-modulated radiotherapy

Linac; Linear accelerator

of both machines, which has also be seen in the comparison of the measure data. Nevertheless,

Figure 11. Plan verification of an IMRT plan with 6MV FFF, calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 97%

**Figure 11.** Plan verification of an IMRT plan with 6MV FFF, calculated for one machine and treated at the other. The gamma image was evaluated with 3% and 3 mm and showed a passing rate of 97% which is indicated in the histogram

the specification of the manufacturer with a distance to agreement of 3 mm was met.

which is indicated in the histogram below.

182 Evolution of Ionizing Radiation Research

below.

RTPS; Radiotherapy planning system

VMAT; Volumetric-modulated arc therapy

#### **Acknowledgements**

The authors thank Esther Illek for the planning and measurements of some VMAT and IMRT plans.

This work was supported by the German Research Foundation (DFG) within the funding program Open Access Publishing.

#### **Author details**

Marius Treutwein\* , Petra M. Härtl, Christian Gröger, Zaira Katsilieri and Barbara Dobler

\*Address all correspondence to: marius.treutwein@ukr.de

Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany

#### **References**


[7] Hrbacek J, Depuydt T, Nulens A, Swinnen A, Van den Heuvel, Frank. Quantitative evaluation of a beam-matching procedure using one-dimensional gamma analysis. Med Phys 2007;34(7):2917.

**Acknowledgements**

184 Evolution of Ionizing Radiation Research

**Author details**

Marius Treutwein\*

**References**

1946.

Phys 2014;39(4):206–11.

program Open Access Publishing.

\*Address all correspondence to: marius.treutwein@ukr.de

of medical accelerators. Med Phys 2009;36(9):4197–212.

beams in radiation therapy. Med Phys 2012;39(10):6455–64.

ques for IMRT. Med Phys 2011;38(3):1313.

ar accelerators. Med Phys 1993;20(6):1743–46.

plans.

The authors thank Esther Illek for the planning and measurements of some VMAT and IMRT

This work was supported by the German Research Foundation (DFG) within the funding

Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany

[1] Klein EE, Hanley J, Bayouth J, Yin F, Simon W, Dresser S, Serago C, Aguirre F, Ma L, Arjomandy B, Liu C, Sandin C, Holmes T. Task Group 142 report: quality assurance

[2] Low DA, Moran JM, Dempsey JF, Dong L, Oldham M. Dosimetry tools and techni‐

[3] Bissonnette J, Balter PA, Dong L, Langen KM, Lovelock DM, Miften M, Moseley DJ, Pouliot J, Sonke J, Yoo S. Quality assurance for image-guided radiation therapy uti‐ lizing CT-based technologies: a report of the AAPM TG-179. Med Phys 2012;39(4):

[4] Fogliata A, Garcia R, Knoos T, Nicolini G, Clivio A, Vanetti E, Khamphan C, Cozzi L. Definition of parameters for quality assurance of flattening filter free (FFF) photon

[5] Sahani G, Sharma SD, Sharma, P K Dash, Deshpande DD, Negi PS, Sathianarayanan VK, Rath GK. Acceptance criteria for flattening filter-free photon beam from stand‐ ard medical electron linear accelerator: AERB task group recommendations. J Med

[6] Marshall MG. Matching the 6-MV photon beam characteristics of two dissimilar line‐

, Petra M. Härtl, Christian Gröger, Zaira Katsilieri and Barbara Dobler


**Detection and Measurement**

[21] Commissioning and quality assurance of computerized planning systems for radia‐ tion treatment of cancer. 2004. Vienna: International Atomic Energy Agency (Techni‐

[22] Nucletron. Radiation Commissioning and Quality Assurance. Nucletron, Veenen‐ daal, NL (Oncentra External Beam v4.3 Oncentra Brachy v4.3, 192.740ENG-08). [23] Mijnheer B, Olszewska A, Fiorino C, Hartmann G, Knöös T, Rosenwald J, Welle‐ weerd H. Quality Assurance of Treatment Planning Systems—Practical Examples for Non-IMRT Photon Beams. 2004. Brussels, Belgium: ESTRO (ESTRO Booklet, 7). [24] Nucletron. User Manual. Nucletron, Veenendaal, NL (Oncentra External Beam v4.3

[25] Low DA, Harms WB, Mutic S, Purdy JA. A technique for the quantitative evaluation

[26] Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit30.11.2011. Strahlenschutz in der Medizin—Richtlinie zur Verordnung über den Schutz vor

[27] Board of Faculty of Clinical Oncology. The timely delivery of radical radiotherapy: standards and guidelines for the management of unscheduled treatment interrup‐ tions. 3. Aufl. The Royal College of Radiologists; 2008. http://www.rcr.ac.uk/docs/

[28] Treutwein M, Hipp M, Koelbl O, Dobler B. Searching standard parameters for volu‐ metric modulated arc therapy (VMAT) of prostate cancer. Radiat Oncol 2012;7108. [29] Paynter D, Weston SJ, Cosgrove VP, Evans JA, Thwaites DI. Beam characteristics of energy-matched flattening filter free beams. Med Phys 2014;41(5):052103.

[30] Huang Y, Siochi RA, Bayouth JE. Dosimetric properties of a beam quality-matched 6

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Oncentra Brachy v4.3, 192.729ENG-08).

Schäden durch ionisierende Strahlen.

of dose distributions. Med Phys 1998;25(5):656–61.

oncology/pdf/BFCO%2808%296\_Interruptions.pdf.

#### **Chapter 8**

## **Ionizing Radiation Detectors**

#### Marcia Dutra R. Silva

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60914

#### **Abstract**

Ionizing radiation has always been present in the natural environment. However, this radiation is not easily detected and since it also possesses high ionizing power and penetration strength, it constitutes a risk to human health when it is found outside of its acceptable limits. The adverse effects of ionizing radiation on human health need to be systematically monitored in order to prevent damage, overexposure, or even death. The detection of the radiation depends on its particular interaction with a sensitive material, and different types of detectors, in different physical states (solid, liquid or gas), are used to measure selective types of ionizing radiation. New materials such as organic semiconductors, for instance, are being targeted for research and as potential candidates for new perspectives on ionizing radiation sensing.

**Keywords:** Radiation, high energy, detector

#### **1. Introduction**

Ionizing radiation has always been present in the natural environment. Sources of ionizing radiation are commonly found in water, air, soil, or manmade devices. However, ionizing radiation is situated in the electromagnetic spectrum outside the region of perception of the human eye - visible region - and it has no smell. Thus, it cannot be detected by the human senses. Since the ionizing radiation is not easily detected and it also possesses high ionizing power and penetration strength, it constitutes a risk to human health when it is found outside of its acceptable limits. The adverse effects of ionizing radiation on human health need to be systematically monitored in order to prevent damage, overexposure, or even death. The ability to identify sources of radiation, specific radioisotopes, and measure quantities of radiation is

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

crucial to environmental monitoring, radiation protection, and development of security programs.

Ionizing radiation cannot be directly measured. The detection is done indirectly using an ionizing radiation sensitive material, which constitutes the basis when developing sensors or detectors of radiation. However, there is not a radiation detector that can measure all types of radiation efficiently. The interaction of radiation with matter depends on the nature of the radiation: the electromagnetic radiation, light charged particles, neutrons, or heavy charged particles. Therefore, a detector which efficiently measures a particular kind of radiation could be completely inappropriate for others. The nature of the sensitive material's response to the ionizing radiation and its energy range to be measured will determine the type of detector.

When the ionizing radiation interacts with a sensitive material constituting the detector device, it generates a signal, which can be a pulse, hole, light signal, and many others [1]. The detection of the radiation depends on the particular interactions with the sensitive material, and there are three main and well-established possibilities to relate and categorize the induced radiation with the generated signal in the detector, as shown below:


*A priori* or *a posteriori* application of ionizing radiation detector will indicate which type is more suitable to use for a specific measurement. To measure the radiation in real time, as in the case of evaluating the average radiation of a given location, direct-read instruments such as gas detectors, scintillation detectors, or semiconductor detectors are used. In order to measure the radiation to which a person is exposed, detectors that can be further processed such as photographic emulsions and thermoluminescent dosimeters are used.

Radiation detectors have to two key principles: (i) ionization and (ii) excitation. In ionizationbased detectors, electron-ion pairs are generated by enough energy when ionizing radiation reaches atoms of a sensitive material and removes orbital electrons (Figure 1).

**Figure 1.** Ionization Process.

In excitation-based detectors, bounded electrons are raised to an excited state in the atom or molecule when part of the radiation energy is transferred to them (Figure 2). The electron excited to these states returns to its ground state emitting light in the UV-Visible region.

**Figure 2.** Excitation process.

#### **2. Detectors**

crucial to environmental monitoring, radiation protection, and development of security

Ionizing radiation cannot be directly measured. The detection is done indirectly using an ionizing radiation sensitive material, which constitutes the basis when developing sensors or detectors of radiation. However, there is not a radiation detector that can measure all types of radiation efficiently. The interaction of radiation with matter depends on the nature of the radiation: the electromagnetic radiation, light charged particles, neutrons, or heavy charged particles. Therefore, a detector which efficiently measures a particular kind of radiation could be completely inappropriate for others. The nature of the sensitive material's response to the ionizing radiation and its energy range to be measured will determine the type of detector.

When the ionizing radiation interacts with a sensitive material constituting the detector device, it generates a signal, which can be a pulse, hole, light signal, and many others [1]. The detection of the radiation depends on the particular interactions with the sensitive material, and there are three main and well-established possibilities to relate and categorize the induced radiation

**i.** The generated signal from the incident radiation is created by the counting of the

**ii.** The incident radiation generates a signal that measures the energy that has reached

**iii.** The detector measures the average energy incident on a specific point of the sensitive

*A priori* or *a posteriori* application of ionizing radiation detector will indicate which type is more suitable to use for a specific measurement. To measure the radiation in real time, as in the case of evaluating the average radiation of a given location, direct-read instruments such as gas detectors, scintillation detectors, or semiconductor detectors are used. In order to measure the radiation to which a person is exposed, detectors that can be further processed such as

Radiation detectors have to two key principles: (i) ionization and (ii) excitation. In ionizationbased detectors, electron-ion pairs are generated by enough energy when ionizing radiation

number of interactions occurring at the sensitive volume of the detector. In this case,

volume, that is, the absorbed radiation dose. Such detectors are known as *dosimeters*.

with the generated signal in the detector, as shown below:

the detector. The detector is named *spectrometer*.

photographic emulsions and thermoluminescent dosimeters are used.

reaches atoms of a sensitive material and removes orbital electrons (Figure 1).

the detector is called *counter*.

**Figure 1.** Ionization Process.

programs.

190 Evolution of Ionizing Radiation Research

#### **2.1. Gas-filled detectors**

When a high-energy radiation passes through a medium, it undergoes ionization and releases charges that depend on the excitation radiation energy. In gas detectors, the ionization appears as electron-ion pairs and these charge carriers can be attracted and collected by electrodes [2-4].

In gases, ionized particles can travel more freely than in a liquid or a solid. Therefore, in gas counters the space between the electrodes is filled with a gas and when a voltage is applied an electric field is created by the potential difference between the electrodes. Electrons and positively charged gas atom of each ion pair accelerate to anode and cathode, respectively, resulting in an electric signal (current) in the circuit that can be correlated to radiation exposure and displayed as a value (Figure 3).

**Figure 3.** Current mode.

Another detection possibility is to acquire the incident radiation signal through pulses (pulse counting mode). In this case, the number of ion-electron pairs generated corresponds to the intensity of the detected pulse (Figure 4). The ionization chamber, proportional counters, and Geiger-Muller counters are examples of gas detectors. Typically, ionization chambers are used in the current mode while proportional counters and Geiger-Muller use the pulse mode to measure the radiation.

**Figure 4.** Pulse mode counting.

The average energy W required to produce an electron-ion pair varies (20-45eV) depending on the gas used. The average energy W can be expressed as [5]:

$$\mathcal{W} = \frac{E\_i}{\{N\}} \tag{1}$$

where *Ei* is the energy deposited by the incident radiation and N the average number of electron-ion pairs formed.

The number of ion pairs generated varies according to the applied voltage for constant incident radiation. The voltages can vary widely depending upon the detector geometry and the gas type and pressure. The different voltage regions are indicated schematically in Figure 5. There are six main practical operating regions, where three are useful to detect ionizing radiation.

**Region (1):** At low voltage, the electric field is not large enough to accelerate electrons and ions. Then, many electrons and ions produced in gas recombine before they reach the electro‐ des and they are not collected. In this area, the size pulse increases as applied voltage increases, and the recombination rate decreases to the point where it becomes zero. This first region is called recombination and is not useful for counting radiation.

**Region (2):** In the ionization region, the voltage is high enough and each ion pair generated reaches the electrodes. However, the number of the ion pairs does not change when voltage is increased and the curve is flat. Then, the number of ion pairs produced by the radiation is nearly equal to the number of ion pairs collected by the electrodes because there is no recom‐

**Figure 5.** Six-region curve for gas-filled detectors.

bination and the voltage is not high enough to produce gas amplification. The ionization chambers work in this region.

**Region (3):** In the proportional region, there is a gas amplification that causes more ion pairs to reach the electrodes than ion pairs are initially produced by radiation. The electrons from the primary ionization acquire enough energy between collisions to produce additional ionizations due to strong electric field. These secondary ions formed are also accelerated causing an effect known as Townsend avalanches, which creates a single large electrical pulse.

Primary ionization

Another detection possibility is to acquire the incident radiation signal through pulses (pulse counting mode). In this case, the number of ion-electron pairs generated corresponds to the intensity of the detected pulse (Figure 4). The ionization chamber, proportional counters, and Geiger-Muller counters are examples of gas detectors. Typically, ionization chambers are used in the current mode while proportional counters and Geiger-Muller use the pulse mode to

The average energy W required to produce an electron-ion pair varies (20-45eV) depending

The number of ion pairs generated varies according to the applied voltage for constant incident radiation. The voltages can vary widely depending upon the detector geometry and the gas type and pressure. The different voltage regions are indicated schematically in Figure 5. There are six main practical operating regions, where three are useful to detect ionizing radiation.

**Region (1):** At low voltage, the electric field is not large enough to accelerate electrons and ions. Then, many electrons and ions produced in gas recombine before they reach the electro‐ des and they are not collected. In this area, the size pulse increases as applied voltage increases, and the recombination rate decreases to the point where it becomes zero. This first region is

**Region (2):** In the ionization region, the voltage is high enough and each ion pair generated reaches the electrodes. However, the number of the ion pairs does not change when voltage is increased and the curve is flat. Then, the number of ion pairs produced by the radiation is nearly equal to the number of ion pairs collected by the electrodes because there is no recom‐

is the energy deposited by the incident radiation and N the average number of

*<sup>N</sup>* (1)

<sup>=</sup> *<sup>i</sup> <sup>E</sup> <sup>W</sup>*

on the gas used. The average energy W can be expressed as [5]:

called recombination and is not useful for counting radiation.

measure the radiation.

192 Evolution of Ionizing Radiation Research

**Figure 4.** Pulse mode counting.

electron-ion pairs formed.

where *Ei*

$$\mathbf{X} + \mathbf{P} = \mathbf{X}^+ + \mathbf{P} + \mathbf{e}^-$$

Secondary ionization

$$\mathbf{X} + \mathbf{e}^- = \mathbf{X}^+ + \mathbf{e}^- + \mathbf{e}^-$$

where X is the gas atom, p is the charge particle traversing the gas, and e is the electron.

The number of ion pairs collected divided by the number of ion pairs produced by the primary ionization provides the gas amplification factor. For example, if 50, 000 ion pairs are collected and 10, 000 ion pairs were initially produced, the gas amplification factor is 5. The gas amplification factor varies according to the applied voltage across the electrodes and it also varies with the geometry of the detector. However, it is constant at a specific voltage and for any kind of radiation or energy of radiation. Then, if a voltage increases the gas amplification factor increases proportionally, but if a voltage remains constant the gas amplification factor also does not change. Because of this amplification process, proportional counters are ex‐ tremely sensitive (<10KeV) while ionization chambers are limited by discriminate particles of >10 keV energy.

The pulse height depends on the detected particle energy. Therefore, different energies of radiation can be distinguished by analyzing the pulse height. For instance, the size pulse from an alpha particle, for a fixed applied voltage, will be larger than the signal from a beta particle. Thus, particle identification and energy measurement are possible by using proportional counters.

**Region (4):** In the limited proportional region, the gas amplification factor is not constant for a given voltage setting and there is no proportionality of the output signal to the deposited energy at a given applied voltage. Additional avalanches occur, leading to additional ioniza‐ tions and nonlinear effects take place. The nonlinearities observed are due to the high positive ion concentration, which leads to distortion in the electric field. Free electrons due to their high mobility are quickly collected by the electrodes while positive ions are slowly moving. Then, clouds of positive ions are created near the electrode, leading to distortions in gas multiplica‐ tion. This region is usually avoided as a detection region.

**Region (5):** At high voltages, the electric field is so strong that avalanches of electron-ion pairs are produced and reach the electrodes. A strong signal is produced by these avalanches with shape and height independently of the primary ionization and the energy of the detected photon. This region is called the Geiger-Muller region, and the large output pulse is the same for all photons. Therefore, the energy or even incident radiation particle cannot not be distinguished by GM detectors.

**Region (6):** At still higher voltages (above GM region), the electric field strength is so intense that it itself produces ionization in the gas and completes avalanching. Continuous electric discharges occur between the electrodes and the detectors that operate in this region can be damaged. Therefore, no practical detection of radiation is possible.

#### **2.2. Scintillation detectors**

Scintillators are materials that exhibit luminescence when excited with ionizing radiation. The scintillation mechanism can be explained by means of the energy-band theory. In this model, a band gap separates the valence band (filled band) of conduction band (usually empty). Thus, via the ionization process, an electron can be excited from the valence band to the conduction band or to the energy states located close to the mid-gap (impurities). An exciton is formed when the electron removed remains electrostatically bonded with the hole left in the valence band. The electron excited to these states decays to the ground state emitting light in the visible range of the electromagnetic spectrum [6]. This visible light interacts with the photocathode and electrons are emitted by photoelectric effect and/or Compton scattering, producing a current in the circuit. However, scintillation detectors produce currents of low intensity and only after the advent of photomultiplier tubes has its use become feasible. In this way, the electrons emitted by photocathode are multiplied by the dynodes in the photomultiplier tube and collected in the anode. As a result, a measurable electrical current is acquired. The output pulse of electrons of a scintillation detector is proportional to the energy of the original radiation.

any kind of radiation or energy of radiation. Then, if a voltage increases the gas amplification factor increases proportionally, but if a voltage remains constant the gas amplification factor also does not change. Because of this amplification process, proportional counters are ex‐ tremely sensitive (<10KeV) while ionization chambers are limited by discriminate particles of

The pulse height depends on the detected particle energy. Therefore, different energies of radiation can be distinguished by analyzing the pulse height. For instance, the size pulse from an alpha particle, for a fixed applied voltage, will be larger than the signal from a beta particle. Thus, particle identification and energy measurement are possible by using proportional

**Region (4):** In the limited proportional region, the gas amplification factor is not constant for a given voltage setting and there is no proportionality of the output signal to the deposited energy at a given applied voltage. Additional avalanches occur, leading to additional ioniza‐ tions and nonlinear effects take place. The nonlinearities observed are due to the high positive ion concentration, which leads to distortion in the electric field. Free electrons due to their high mobility are quickly collected by the electrodes while positive ions are slowly moving. Then, clouds of positive ions are created near the electrode, leading to distortions in gas multiplica‐

**Region (5):** At high voltages, the electric field is so strong that avalanches of electron-ion pairs are produced and reach the electrodes. A strong signal is produced by these avalanches with shape and height independently of the primary ionization and the energy of the detected photon. This region is called the Geiger-Muller region, and the large output pulse is the same for all photons. Therefore, the energy or even incident radiation particle cannot not be

**Region (6):** At still higher voltages (above GM region), the electric field strength is so intense that it itself produces ionization in the gas and completes avalanching. Continuous electric discharges occur between the electrodes and the detectors that operate in this region can be

Scintillators are materials that exhibit luminescence when excited with ionizing radiation. The scintillation mechanism can be explained by means of the energy-band theory. In this model, a band gap separates the valence band (filled band) of conduction band (usually empty). Thus, via the ionization process, an electron can be excited from the valence band to the conduction band or to the energy states located close to the mid-gap (impurities). An exciton is formed when the electron removed remains electrostatically bonded with the hole left in the valence band. The electron excited to these states decays to the ground state emitting light in the visible range of the electromagnetic spectrum [6]. This visible light interacts with the photocathode and electrons are emitted by photoelectric effect and/or Compton scattering, producing a current in the circuit. However, scintillation detectors produce currents of low intensity and only after the advent of photomultiplier tubes has its use become feasible. In this way, the

tion. This region is usually avoided as a detection region.

damaged. Therefore, no practical detection of radiation is possible.

distinguished by GM detectors.

**2.2. Scintillation detectors**

>10 keV energy.

194 Evolution of Ionizing Radiation Research

counters.

A good scintillator material is highly efficient in converting incident radiation energy into light. The scintillator must also be transparent to its own light emissions and it must have a short decay time because the transparence is important to a good light transmission to reach the electrode, and the short decay time allows fast response.

Decay time is the time required for scintillation emission to decrease to e-1 of its maximum and it can be described as the sum of two exponential components [7, 8]:

$$\dot{\mathbf{u}}\left(t\right) = \frac{\alpha \nu}{\tau\_0} e^{-\frac{\lambda t}{\lambda \tau\_0}} + \frac{1 - \alpha \nu}{\tau\_1} e^{-\frac{\lambda t}{\lambda \tau\_1}}\tag{2}$$

where *τ*0 and *τ*<sup>1</sup> are the decay time constants of the fast and slow components of a scintillator, respectively, and ω is the weight of the fast component.

The fast component is related to the fluorescence and the slow component is related to phosphorescence or afterglow. These two types of radiative processes (photon emission processes) are well-established in the literature and they are illustrated by the Perrin-Jablonski diagram in Figure 6. The fluorescence occurs in the de-excitation process between singlet electronic states (same spin multiplicity), and it is responsible for the majority of emitting radiative processes due to short decay time (10-9s). The phosphorescence occurs in deexcitation process between different multiplicity states (triplet-singlet), in times the order of 10-3s. The singlet states are represented by Sn and triplet states by Tn, where n = 0, 1, 2, 3..., and n = 0 corresponds to the ground state [8, 9]. Other type of delayed emission is the delayed fluorescence (DF), which is a reverse intersystem crossing T1->S1, it is induced thermally or by collisions. Afterglow competes with the scintillation process leading to a decrease of total efficiency of conversion of ionizing radiation into light, and it should be avoided in scintillation detectors [10].

Scintillation detectors are composed of two basic types of detector materials: organic and inorganic. Inorganic scintillators have scintillation properties due to their crystalline structure or due to activators (impurities), which enable scintillation process. Organic scintillators do not need crystal structure or activators because each molecule can act as a scintillation center. The difference in their behavior comes to the different ranges of energy levels excited by the incident radiation. Inorganic scintillators usually respond more slowly than organic scintilla‐ tors, but they are more efficient than organic materials for detecting ionizing radiation because of their greater density and higher average atomic number. However, organic materials are more flexible and cheaper than inorganic material, leading to numerous scientific efforts to increase their performance in recent decades.

**Figure 6.** Perrin-Jablonski diagram.

Currently, the scintillation detectors have excellent sensitivity to excitation energy and fast response time. Different types of scintillators, in different physical states (solid, liquid, or gas), are used to measure selective types of ionizing radiation. They are widely used in medical applications for image generation (X-rays and tomography), as well as high-energy physics experiments, plant laboratories, airports security (X-rays machines), and radiation sensing for nuclear installations.

#### **2.3. Semiconductor detectors**

Semiconductors are materials, inorganic or organic, which have the ability to control their electronic conduction depending on chemical structure, temperature, illumination, and presence of dopants. The name semiconductor comes from the fact that these materials usually present an intermediate conductivity between conductors and insulators. Consequently, they have an energy gap less than 4eV [11]. In solid-state physics, energy gap or band gap is an energy range between valence band and conduction band where electron states are forbidden. The valence band is the region where electrons are connected to the lattice atoms. The conduction band is the region that contains the energy levels where free electrons can move through the crystal structure [12, 13]. The width of the forbidden energy band is what categorizes the material as conductor, semiconductor, or insulator (Figure 7).

There are many semiconductors in nature and others synthesized in laboratories; however, the best known are silicon (Si) and germanium (Ge). Silicon has been considered precursor to the revolution that has occurred in recent decades in the electronic area. However, germanium is more used than silicon for radiation detection because the average energy necessary to create an electron-hole pair is 3, 6eV for silicon and 2, 6eV for germanium, which provides the latter a better resolution in energy. In addition, in gamma spectroscopy, germanium is preferred due to its atomic number being much higher than silicon and which increases the probability of γ-ray interaction.

**Figure 7.** Band structure for electron energies in solids.

Currently, the scintillation detectors have excellent sensitivity to excitation energy and fast response time. Different types of scintillators, in different physical states (solid, liquid, or gas), are used to measure selective types of ionizing radiation. They are widely used in medical applications for image generation (X-rays and tomography), as well as high-energy physics experiments, plant laboratories, airports security (X-rays machines), and radiation sensing for

Semiconductors are materials, inorganic or organic, which have the ability to control their electronic conduction depending on chemical structure, temperature, illumination, and presence of dopants. The name semiconductor comes from the fact that these materials usually present an intermediate conductivity between conductors and insulators. Consequently, they have an energy gap less than 4eV [11]. In solid-state physics, energy gap or band gap is an energy range between valence band and conduction band where electron states are forbidden. The valence band is the region where electrons are connected to the lattice atoms. The conduction band is the region that contains the energy levels where free electrons can move through the crystal structure [12, 13]. The width of the forbidden energy band is what

There are many semiconductors in nature and others synthesized in laboratories; however, the best known are silicon (Si) and germanium (Ge). Silicon has been considered precursor to the revolution that has occurred in recent decades in the electronic area. However, germanium is more used than silicon for radiation detection because the average energy necessary to create

categorizes the material as conductor, semiconductor, or insulator (Figure 7).

nuclear installations.

**2.3. Semiconductor detectors**

**Figure 6.** Perrin-Jablonski diagram.

196 Evolution of Ionizing Radiation Research

In semiconductor detectors, also called solid-state detectors, charge carriers are produced and collected by electrodes as in ionization chambers. However, the charge carriers are electrons and holes and not electrons and ions as in ionization chambers. When semiconductor detectors are subjected to high-energy radiation, electron-hole pairs are produced and converted into electric current.

The electron mobility in a gas counter is thousands of times greater than that of the ions. In fact, the electron mobility in semiconductors is roughly equal that of the holes and both types of carriers contribute to conductivity.

Conductivity is the inverse of resistivity and it is defined by

$$
\mathbf{J} = \sigma \mathbf{E} \tag{3}
$$

where *J* is the current density (A/m2), *σ* is the conductivity [A/(V.m)], and *E* is the electric field (V/m).

Another expression for the current density is:

$$J = eN\sigma$$

where *N* is the number of charge carriers, *e* is the elementary charge, and *v* is the speed of carriers.

The following equation is obtained by using Equations 3 and 4:

$$
\sigma = eN\frac{\upsilon}{E} \tag{5}
$$

The ratio **υ***/E* is called carrier mobility µ:

$$
\mu = \frac{\upsilon}{E} \tag{6}
$$

The expression for the conductivity becomes:

$$
\sigma = e \left( N\_e \,\,\mu\_e + N\_h \mu\_h \right) \tag{7}
$$

where *Ne* and *Nh* are carrier concentrations and *μe* and *μh* are the mobilities of electrons and holes, respectively, and according to this equation, the conductivity changes if the mobility of charge carriers and/or their concentrations change. Thus, both terms in the right-hand side of Equation 7 contribute to the conduction in semiconductor detectors.

A small energy is required to create an electron-hole pair in semiconductor materials (~3 eV for germanium) compared to the energy needed to create an electron-ion pair in gases (~30 eV for typical gas detectors) or to create an electron-hole pair in scintillators (~100eV) [14]. As a consequence, a great number of electron-hole pairs are produced and reach the electrodes, increasing the number of pairs per pulse and, then, decreasing both statistical fluctuation and signal/noise in the preamplifier. This generates a big advantage over other detectors and the output pulse provides much better energy resolution. Moreover, the small sensitive area used to detect radiation (few millimeters) and the high speed of charge carriers provide an excellent charge collection time (~10-7 s).

The energy resolution, R, determines the ability of the system to distinguish two energies that are very close to each other, and that constitute an important parameter in the spectral detection of ionizing radiation (Figure 8). It is commonly defined as:

$$R = \frac{FWHM}{H\_0} \tag{8}$$

where FWHM is the full-width-at-half-maximum and H0 is the peak centroid.

In order for a semiconductor to act as a radiation detector, the active area to radiation must be free of excess electrical charges (depleted). The depletion region can be formed through the use of very high purity materials like High Purity germanium (HPGe) or PN junctions. PN junctions are obtained when an n-type semiconductor (excess of electrons) is placed in contact with a p-type semiconductor (excess of holes). Then, electrons and holes diffuse from n-region to p-region and from p-region to n-region, respectively, and they recombine around the interface. The ions, which are left behind by electrons and holes that were recombined, create an electric field that will attract more electrons and holes until there is no more charge carriers to recombine (Figure 9).

**Figure 8.** FWHM for a Gaussian distribution. In this case, the FWHM results related to the σ as FWHM *= 2.35* σ.

At this moment, if the ionizing radiation interacts with the semiconductor in this depleted region, electrons are raised to the conduction band leaving behind holes in the valence band and producing a large number of electron-hole pairs. If a voltage is applied across the semi‐ conductor, these carriers are readily attracted to the electrodes and current flows into circuit resulting in a pulse. The size of the pulse is directly proportional to the number of carriers collected, which is proportional to the energy deposited in the material by the incident radiation.

**Figure 9.** PN junction.

The ratio **υ***/E* is called carrier mobility µ:

198 Evolution of Ionizing Radiation Research

The expression for the conductivity becomes:

charge collection time (~10-7 s).

to recombine (Figure 9).

m<sup>=</sup> *<sup>v</sup>*

> mm

where *Ne* and *Nh* are carrier concentrations and *μe* and *μh* are the mobilities of electrons and holes, respectively, and according to this equation, the conductivity changes if the mobility of charge carriers and/or their concentrations change. Thus, both terms in the right-hand side of

A small energy is required to create an electron-hole pair in semiconductor materials (~3 eV for germanium) compared to the energy needed to create an electron-ion pair in gases (~30 eV for typical gas detectors) or to create an electron-hole pair in scintillators (~100eV) [14]. As a consequence, a great number of electron-hole pairs are produced and reach the electrodes, increasing the number of pairs per pulse and, then, decreasing both statistical fluctuation and signal/noise in the preamplifier. This generates a big advantage over other detectors and the output pulse provides much better energy resolution. Moreover, the small sensitive area used to detect radiation (few millimeters) and the high speed of charge carriers provide an excellent

The energy resolution, R, determines the ability of the system to distinguish two energies that are very close to each other, and that constitute an important parameter in the spectral detection

> 0 *FWHM <sup>R</sup>*

In order for a semiconductor to act as a radiation detector, the active area to radiation must be free of excess electrical charges (depleted). The depletion region can be formed through the use of very high purity materials like High Purity germanium (HPGe) or PN junctions. PN junctions are obtained when an n-type semiconductor (excess of electrons) is placed in contact with a p-type semiconductor (excess of holes). Then, electrons and holes diffuse from n-region to p-region and from p-region to n-region, respectively, and they recombine around the interface. The ions, which are left behind by electrons and holes that were recombined, create an electric field that will attract more electrons and holes until there is no more charge carriers

=

where FWHM is the full-width-at-half-maximum and H0 is the peak centroid.

s

Equation 7 contribute to the conduction in semiconductor detectors.

of ionizing radiation (Figure 8). It is commonly defined as:

*<sup>E</sup>* (6)

*<sup>H</sup>* (8)

= + *eN N* ( *e e hh* ) (7)

In semiconductors, if the temperature increases, electrons can be thermally excited from the valence band to the conduction band. Consequently, some semiconductor detectors must be cooled so as to reduce the number of electron-hole pairs in the crystal in the absence of radiation. Although solid-state detectors can be manufactured much smaller size than those of equivalent gas-filled detectors and they have short response time, seconds compared to the hours of TLD detectors, they are still expensive because they need to be cooled. Thus, they are used when higher resolution is required; if higher efficiency is necessary, scintillation detectors are used.

Different semiconductor materials and device arrangements are used, depending on the type of radiation to be measured and the aim of application. The types of radiation that can be measured with semiconductor detectors comprise a large range of the electromagnetic spectrum: <1 eV to ~10 MeV for photons and energies above keV for charged particles. Commonly, semiconductor detectors are employed for beta particles or gamma radiation because the heavy charged particles cause more radiation damage. They are widely used in nuclear power station electronic dosimeters and portable survey instruments in gamma spectroscopy systems.

#### **2.4. Thermoluminescent dosimeters**

The amount of radiation absorbed by the human body can be determined through radiation dosimetry. A dosimeter has to correlate the absorbed radiation with biological effects induced in humans. The physical quantity that quantifies this relationship is called *absorbed dose*. The absorbed dose, D, of any ionizing radiation can be considered as the amount of energy given to the medium by ionizing particles or photons per unit of mass *dm* [2, 14, 15]:

$$D = \frac{d\overline{\epsilon}}{d\mathfrak{m}}\tag{9}$$

where *d*ϵ¯ is the average energy deposited by the radiation on a point P.

The SI unit of absorbed dose is the Gray (Gy), defined as: 1Gy = 1 J/kg. The obsolete units for dose are the rad (radiation absorbed dose) and the centigray (cGy): 1rad = 10-2 J/kg = 1cGy.

Thermoluminescent dosimeters (TLDs) are the foremost used devices for personal dosimetry. They are composed of crystal devices that emit light when are heated. The TLD reading device is able to calculate the amount of light released during heating, which can then be correlated with the absorbed dose received and stored by the TLD dosimeter.

A useful model of the thermoluminescence mechanism is provided in terms of the band model for solids. Thus, when a thermoluminescent crystal is exposed to ionizing radiation, electrons are quickly promoted to their conduction band through direct excitation process. However, some electrons are trapped by metastable states and when the material is subjected to thermal stimulation, they have enough energy to leave the trap states and recombine with holes that were left in the valence band. The excess of energy in this process is conserved by radiative deactivations emitting light, which is proportional to the absorbed ionized dose [16].

Figure 10 shows a model of energy bands with electronic transitions in thermoluminescence process.

hours of TLD detectors, they are still expensive because they need to be cooled. Thus, they are used when higher resolution is required; if higher efficiency is necessary, scintillation detectors

Different semiconductor materials and device arrangements are used, depending on the type of radiation to be measured and the aim of application. The types of radiation that can be measured with semiconductor detectors comprise a large range of the electromagnetic spectrum: <1 eV to ~10 MeV for photons and energies above keV for charged particles. Commonly, semiconductor detectors are employed for beta particles or gamma radiation because the heavy charged particles cause more radiation damage. They are widely used in nuclear power station electronic dosimeters and portable survey instruments in gamma

The amount of radiation absorbed by the human body can be determined through radiation dosimetry. A dosimeter has to correlate the absorbed radiation with biological effects induced in humans. The physical quantity that quantifies this relationship is called *absorbed dose*. The absorbed dose, D, of any ionizing radiation can be considered as the amount of energy given

to the medium by ionizing particles or photons per unit of mass *dm* [2, 14, 15]:

¯ is the average energy deposited by the radiation on a point P.

with the absorbed dose received and stored by the TLD dosimeter.

= *d d D*

*m*

The SI unit of absorbed dose is the Gray (Gy), defined as: 1Gy = 1 J/kg. The obsolete units for dose are the rad (radiation absorbed dose) and the centigray (cGy): 1rad = 10-2 J/kg = 1cGy.

Thermoluminescent dosimeters (TLDs) are the foremost used devices for personal dosimetry. They are composed of crystal devices that emit light when are heated. The TLD reading device is able to calculate the amount of light released during heating, which can then be correlated

A useful model of the thermoluminescence mechanism is provided in terms of the band model for solids. Thus, when a thermoluminescent crystal is exposed to ionizing radiation, electrons are quickly promoted to their conduction band through direct excitation process. However, some electrons are trapped by metastable states and when the material is subjected to thermal stimulation, they have enough energy to leave the trap states and recombine with holes that were left in the valence band. The excess of energy in this process is conserved by radiative

Figure 10 shows a model of energy bands with electronic transitions in thermoluminescence

deactivations emitting light, which is proportional to the absorbed ionized dose [16].

<sup>ò</sup> (9)

are used.

where *d*

process.

ϵ

spectroscopy systems.

200 Evolution of Ionizing Radiation Research

**2.4. Thermoluminescent dosimeters**

**Figure 10.** Model of energy bands in thermoluminescence process. (a) excitation and generation of electron-hole pair, (b) trapping, (c) de-trapping by thermal stimulation, (d) recombination. T is the center of the trap, R is the recombina‐ tion center, EF is the Fermi level, and Eg is the bandgap.

The heating of the TLD dosimeter to assess the accumulated radiation dose is done in tem‐ perature ramps and each temperature value is associated with a value of the light intensity (Figure 11). Thus, through thermoluminescence photons emission it is feasible to establish a curve of thermoluminescence intensity versus temperature that is called TL glow curve. The area under the TL glow curve is directly proportional to the number of emitted photons and, thereby, proportional to radiation dose received.

**Figure 11.** TL glow curve of LiF:Mg, Ti measured with a TLD reader at a low heating rate.

Thermoluminescent crystals possess good levels of deeper traps that require greater thermal energy to release the carrier, thus they can accumulate energy for a longer period of time. Many materials are purposely doped to create impurity levels; others such as LiF (lithium fluoride) already have natural impurities and intrinsic defects. Other substances are used as materials for thermoluminescent dosimetry, for example, CaSO4:Dy (calcium sulfate doped with dysprosium); the CaSO4:Mn (calcium sulfate doped with manganese); and CaF2 (fluorite).

A thermoluminescent crystal can be used as dosimeter only if it presents high emission efficiency, good stability on temperature ranges of work, high resistance to environmental variations and linear radiation dose-response.

The principal advantages of TLD dosimeters are:


Among the disadvantages are:


#### **2.5. Chemical detectors**

In chemical dosimetry, the ionizing radiation produces chemical changes in the medium that can be measured by using a suitable measuring system. Oxidation, reduction, and chemical dissociation are the principal mechanisms of chemical detectors.

The intensity of these changes is characterized by radiation chemical yield (G), which is defined as a number of molecules, ions, atoms, or free radicals of product or dissolved reaction components for 100 eV of absorbed energy, or even defined as the mean number of moles produced/destroyed by mean energy transmitted to the matter [2]:

$$G = \frac{\overline{n}}{\overline{E}} \tag{10}$$

where *n*¯ is the mean moles number and *E*¯ is the mean transmitted energy. *G* SI unit is mol.J-1.

The most widely used chemical dosimetry standard is the Fricke dosimeter. The Fricke dosimetry system provides a reliable means for measurement of absorbed dose to water by ferrous ions oxidation. The dosimeter consists of a solution with 1 mmol/l ferrous sulfate (or ferrous ammonium sulfate), 1 mol/l NaCl, and 0.4 mol/l sulfuric acid. When the Frick solution is irradiated, the ferrous ions, Fe2+, are oxidized by radiation to ferric ions, Fe3+ [17]. The ferric ion concentration is determined by spectrophotometry, which measures absorption peaks at wavelengths of 224 nm and 304 nm. In this case, G-value is defined as the number of moles of ferric ions produced per joule of the energy absorbed in the solution. The usual range of the Fricke dosimeter is from 30Gy to 400 Gy.

#### **2.6. Calorimetric detectors**

A thermoluminescent crystal can be used as dosimeter only if it presents high emission efficiency, good stability on temperature ranges of work, high resistance to environmental

In chemical dosimetry, the ionizing radiation produces chemical changes in the medium that can be measured by using a suitable measuring system. Oxidation, reduction, and chemical

The intensity of these changes is characterized by radiation chemical yield (G), which is defined as a number of molecules, ions, atoms, or free radicals of product or dissolved reaction components for 100 eV of absorbed energy, or even defined as the mean number of moles

where *n*¯ is the mean moles number and *E*¯ is the mean transmitted energy. *G* SI unit is mol.J-1.

The most widely used chemical dosimetry standard is the Fricke dosimeter. The Fricke dosimetry system provides a reliable means for measurement of absorbed dose to water by ferrous ions oxidation. The dosimeter consists of a solution with 1 mmol/l ferrous sulfate (or ferrous ammonium sulfate), 1 mol/l NaCl, and 0.4 mol/l sulfuric acid. When the Frick solution is irradiated, the ferrous ions, Fe2+, are oxidized by radiation to ferric ions, Fe3+ [17]. The ferric ion concentration is determined by spectrophotometry, which measures absorption peaks at

*<sup>E</sup>* (10)

<sup>=</sup> *<sup>n</sup> <sup>G</sup>*

**•** They have high degree of accuracy and precision in the measurements.

**•** The necessary instrumentation for the measurement has high cost.

variations and linear radiation dose-response.

**•** High sensitivity over a wide dosage range.

**•** They are equivalent to human tissues.

**•** Small and varied forms.

202 Evolution of Ionizing Radiation Research

**•** Can be used several times.

Among the disadvantages are: **•** Infeasibility of rereading.

**2.5. Chemical detectors**

The principal advantages of TLD dosimeters are:

**•** Sensitivity varies with the time after irradiation.

**•** They present fading for sensitivity to light and moisture.

dissociation are the principal mechanisms of chemical detectors.

produced/destroyed by mean energy transmitted to the matter [2]:

**•** Readings and the results are not immediate.

Calorimetric methods measure the dose of radiation by measuring the temperature increase in a medium. Although the basic principles of calorimeters are very simple, they have technical problems to ionizing radiation sensing and they have been viewed as complex to make and operate [18]. Small temperature response to low dose of radiation and necessity of extremely thermic isolation are some problems of this type of detector. Therefore, few laboratories use these detectors; however, efforts have been made in order to increase their performance.

#### **2.7. New materials to ionizing radiation sensing**

Despite the well-established known techniques and detectors for ionizing radiation, the field still has a lack of new materials and sensor devices. The use of ionizing radiation in industrial processes, in clinics, hospitals, universities, and research centers has increased considerably and consistently in the past few years. In addition, the inspection and monitoring of aircrews is a current concern and should be mandatory to all flights in the near future. Thus, the development of new materials sensitive to ionizing radiation and robust devices, faster and more accurate, is of crucial importance to this research field and its direct applications.

In the last two decades, there was an effort to combine the energy sensitivity found in semiconductor devices with the low cost and flexibility of organic semiconductor-based conjugated polymers. In this fashion, oligomers and polymers such as PPV (poly p-phenylene vinylene) [19], MEHPPV (poly (2-methoxy, 5- (2 -ethyl-hexoxy) -p-phenylene vinylene) [20, 21], P3HT (poly 3-hexylthiophene) [22, 23], and pentacene [24] have become the target of research and are potential candidates for new perspectives to ionizing radiation sensing. Use of these materials, which have known properties and have been studied, have played an important role in the study of ionizing radiation effects on polymers (Figure 12).

In the interaction of high-energy radiation with semiconductors, primarily there occur excitations and ionizations that generate ions and electrons. The electrons generated (primary electrons) will interact again with the environment and generate secondary excitations that will produce electron-hole pairs. Therefore, the efficiency of the material with the highly energetic radiation will depend on its stopping power or absorption efficiency, the limited capacity of producing electron traps and its ability to grow large areas. Semiconductor polymers generally have high efficiency luminescence and absorption in the UV-Vis region; they can also form films producing large areas, and, hence, they constitute a new alternative in the area of radiation detectors.

In the field of electromagnetic radiation, there are several possible interactions of the most energetic radiation with matter: mainly, the photoelectric effect, Rayleigh scattering, Compton effect, and production of electron-positron pairs. Eventually, these interactions can lead to temporary or permanent modifications. These changes are called effects of degradation. They

**Figure 12.** Chemical structure of polymers: (a) PPV (b) MEHPPV (c) P3HT and (d) pentacene.

may be superficial when there is change only in the physical appearance (color, transparency, etc.) or they may be structural.

Polymer degradation effects have been reported such as scission [25], cross-linking [26, 27], and photobleaching [28]. In scission, there occurs break of the main chain into smaller molecules, reducing its molecular weight. In cross-linking, due to link between two polymer chains or between two big radicals, there is a formation of an insoluble portion with increasing molecular weight. Decrease in viscosity and increase of ductility are effects of scission. Increase of hardness, viscosity, and brittleness are some of the macroscopic effects of cross-linking. Photobleaching occurs when the fluorescent signal of a fluorophore disappears permanently due to photon-induced chemical damage and covalent modification.

Degradation effects are often considered problems such as the oxidation effects of medical implants based on polyethylene after irradiation sterilization, for example[29]. However, the ionizing radiation degradation effects are not sometimes bad results. Many times they are desirable, as in the creation of integrated circuits, decreasing the molecular weight to make a material compatible with the other, in polysaccharides, for use in health care products, cosmetics, textile and food industry, or even to increase viscosity or resistance materials, for instance [30-32].

Polymer interaction with gamma radiation has been studied since the 1970s and different effects have been observed depending on the chemical structure of the polymer and the energy range used for irradiation process. The mechanisms involved in the interaction of gamma radiation with polymers have not been fully elucidated, but changes in conductivity and optical properties have been reported mainly in polyaniline [33] and on PPV and its deriva‐ tives. The results indicate the feasibility of using semiconductor polymers as gamma radiation detectors.

The interest in the use of conductive polymers in this area is due to the adjustability of its luminescence properties and conductivity, and they also have a lower cost than inorganic semiconductors. However, the use of polymers as radiation sensors is recent and few studies are reported in the literature. Among them, the highlighting results are P3HT as the active layer of OLEDs and OFETs for sensing radiation [20], and the MEH-PPV in halogenated solutions for detection of low doses of gamma radiation.

Studies using MEH-PPV have demonstrated that the use of solutions is effectively more sensitive to gamma radiation than solid state. Current knowledge shows that polymeric materials are more sensitive to gamma radiation when solubilized in halogenated solvents [34]. The halogens are well-known to have large cross section for interaction with gamma radiation.

The main results obtained on irradiated P3HT devices were a significant improvement in conductivity with increasing gamma irradiation dose. Polythiophenes irradiated with gamma radiation go to a polaronic state and then stabilized for a bipolaronic and neutral state of the chain, where they remain in the oxidized state. Undoubtedly, the result enables the P3HT as radiation sensor and it leads to a great leap regarding the use of OLEDs and OFETs devices in the space area. However, the order of radiation dose used on P3HT (kGy) is very high for using in personal dosimetry (order of ten grays), for example.

may be superficial when there is change only in the physical appearance (color, transparency,

Polymer degradation effects have been reported such as scission [25], cross-linking [26, 27], and photobleaching [28]. In scission, there occurs break of the main chain into smaller molecules, reducing its molecular weight. In cross-linking, due to link between two polymer chains or between two big radicals, there is a formation of an insoluble portion with increasing molecular weight. Decrease in viscosity and increase of ductility are effects of scission. Increase of hardness, viscosity, and brittleness are some of the macroscopic effects of cross-linking. Photobleaching occurs when the fluorescent signal of a fluorophore disappears permanently

Degradation effects are often considered problems such as the oxidation effects of medical implants based on polyethylene after irradiation sterilization, for example[29]. However, the ionizing radiation degradation effects are not sometimes bad results. Many times they are desirable, as in the creation of integrated circuits, decreasing the molecular weight to make a material compatible with the other, in polysaccharides, for use in health care products, cosmetics, textile and food industry, or even to increase viscosity or resistance materials, for

Polymer interaction with gamma radiation has been studied since the 1970s and different effects have been observed depending on the chemical structure of the polymer and the energy range used for irradiation process. The mechanisms involved in the interaction of gamma radiation with polymers have not been fully elucidated, but changes in conductivity and optical properties have been reported mainly in polyaniline [33] and on PPV and its deriva‐ tives. The results indicate the feasibility of using semiconductor polymers as gamma radiation

due to photon-induced chemical damage and covalent modification.

**Figure 12.** Chemical structure of polymers: (a) PPV (b) MEHPPV (c) P3HT and (d) pentacene.

etc.) or they may be structural.

204 Evolution of Ionizing Radiation Research

instance [30-32].

detectors.

In contrast, studies of MEH-PPV with gamma radiation at this order of dose have shown significant results compatible with personal dosimetry area. However, the results were limited to the use of the polymer in solution, due to the effect being dependent on the solvent. In other words, the effect is indirect: the radiation breaks the solvent chain and the radicals derived from solvent attack break the polymer chain. The attack occurs at the vinylene, breaking the double bond and leading to the conjugation break displayed as blue shift in optical measure‐ ments. This experimental result has been corroborated by theoretical studies and the attack mechanism on vinylene is well-established [35]. Figure 13 shows MEHPPV after ionizing radiation interaction.

**Figure 13.** MEHPPV nonirradiated (0Gy) and irradiated at 30, 60, and 90Gy doses of gamma radiation.

The principal disadvantage of MEH-PPV in the interaction with the gamma radiation is its limitation of use in optoelectronic devices due to the effect of this range of dose not included the utilization in film. Moreover, with the breaking of the chain and the conjugation length, the MEH-PPV has not sufficient extension of conjugation for a good conduction of electrons and neither has any chain doping as P3HT, which is also a limiting factor for their use in optoelectronic devices. Thus, its use is limited as optical sensor radiation in solution and can not be reused. Recalling that, despite limited use, this type of sensor provided an important advance due to measurement method be cheaper and affordable than other types of detectors. Semiconductor detectors based in conjugated polymers do not need be cooled, the instrumen‐ tation used for reading is simple, and polymers are cheaper and easier to process.

### **3. Applications**

In short, a radiation detector is a device used to track, detect, or identify high-energy particles or radiation from natural or artificial sources such as cosmic radiation, nuclear decay, particle accelerators, and X-rays.

Since it is not possible for a single detector to measure all types of radiation efficiently, various types of detectors made of different materials are used in the sensing of specific types of radiation. The main types of radiation detectors and applications are summarized in Table 1.


**Table 1.** Instrument types and its applications.

Despite the variety of sensor devices, the demand for new materials that can detect ionizing radiation efficiently and at as low a cost as possible is essential to the development of this area. In this context, many other materials like polymeric semiconductors, for instance, have been target of research in the last years (section 2). They constitute promising materials for radiation sensing, although no polymeric device for radiation detection is still available for practical use at a large scale.

Unfortunately, the field lacks new sensor devices that are more practical, fast, and accurate for the maintenance and safety of human life in the natural environment as well as in the complex areas of modern civilization.

### **Author details**

the MEH-PPV has not sufficient extension of conjugation for a good conduction of electrons and neither has any chain doping as P3HT, which is also a limiting factor for their use in optoelectronic devices. Thus, its use is limited as optical sensor radiation in solution and can not be reused. Recalling that, despite limited use, this type of sensor provided an important advance due to measurement method be cheaper and affordable than other types of detectors. Semiconductor detectors based in conjugated polymers do not need be cooled, the instrumen‐

In short, a radiation detector is a device used to track, detect, or identify high-energy particles or radiation from natural or artificial sources such as cosmic radiation, nuclear decay, particle

Since it is not possible for a single detector to measure all types of radiation efficiently, various types of detectors made of different materials are used in the sensing of specific types of radiation. The main types of radiation detectors and applications are summarized in Table 1.

rates.

Light emission (solids). Photons; energy spectrometry; e.g., NaI (Tl).

sources).

detectors.

heating. Personal and environmental exposure monitoring.

Germanium detectors.

Direct measurement of exposure or exposure

Alpha particles; detection only (ZnS (Ag)).

Detection of low-energy gamma and beta emitters, for measuring activity (in low-activity

Detection of individual events (alpha and beta particles); e.g., diodes and silicon barrier

Detection and energy measurement of photons or particles; primarily for laboratory use; gamma spectroscopy; X-rays; dosimeters; e.g.,

Detection of individual events, i.e., alpha or beta particles and secondary electrons, for measuring activity (in samples or on surfaces); detecting low intensities of X-rays or gamma radiation.

**Instrument Types Detection Principle Applications**

Light emission (liquid).

**Semiconductor detectors** Ionization, excitation.

**Table 1.** Instrument types and its applications.

**Thermoluminescent detector**

Ionization of air or other gases (ionization chambers).

Ionization of gas with multiplication of electrons in detector (proportional counters and Geiger-Muller).

Excitation of crystal; light release by

**Photographic film** Ionization of Ag Br. Personal exposure monitoring.

tation used for reading is simple, and polymers are cheaper and easier to process.

**3. Applications**

**Gas-filled detectors**

**Scintillators**

**(TLD)**

accelerators, and X-rays.

206 Evolution of Ionizing Radiation Research

Marcia Dutra R. Silva

Address all correspondence to: marciadrs@yahoo.com.br

Materials Spectroscopy Group - GEM, Physics Institute - INFIS, Federal University of Uber‐ landia - UFU, Brazil

#### **References**


[27] Mitsui, H., Hosoi, F. & Kagiya T. Accelerating Effect of Acetylene on the y-Radiation-Induced Cross-Linking of Polyethylene. Polym. J. 1974;6:20-26.

[9] Condon EU. On the Theory of Intensity Distribution in Band Systems. Berkeley: Uni‐

[10] Rodnyi PA. Physical Processes in Inorganic Scintillators. CRC Press 1997, editor. Tay‐

[12] Ashcroft NW, Mermin ND. Solid state physics. Saunders College; 1976. p. 826.

[14] Knoll GF. Radiation Detection and Measurement. 3rd ed. Wiley, editor. 2010. p. 860.

[16] Horowitz YS. Thermoluminescence and thermoluminescent dosimetry. Horowitz YS,

[17] Frick H, Hart EJ. Chemical Dosimetry. In: Attix FH, Roesch WC, editors. Radiat. Dos‐

[18] Kase KR, Bjärngard BE, Attix FH. The Dosimetry of Ionizing Radiation. Academic

[19] Silva MDR, Gançalves AA, Silva R a., Marletta A. Gamma radiation effects on ab‐ sorbance and emission properties of layer-by-layer PPV/DBS films. J. Non. Cryst. Sol‐

[20] Raval HN, Tiwari SP, Navan RR, Rao VR. Determining ionizing radiation using sen‐ sors based on organic semiconducting material. Appl. Phys. Lett. 2009;94:123304.

[21] Silva E a. B, Borin JF, Nicolucci P, Graeff CFO, Netto TG, Bianchi RF. Low dose ioniz‐ ing radiation detection using conjugated polymers. Appl. Phys. Lett. 2005;86:131902.

[22] Zotti G, Zecchin S. Decay of electrochemically injected polarons in polythiophenes.

[23] Wei Z, Xu J, Pu S, Du Y. Electrosyntheses of high-quality freestanding poly(fluoreneco-3-methylthiophene) films with tunable fluorescence properties. J. Polym. Sci. Part

[24] Raval HN, Sutar DS, Nair PR, Rao VR. Investigation of effects of ionizing radiation exposure on material properties of organic semiconducting oligomer - Pentacene.

[25] Thompson LF, Willson CG, Bowden MJ. Introduction to microlithography. American

[26] Mitsui, H., Hosoi, F. & Kagiya T. y-radiation-Induced Cross-Linking of Polyethylene.

Bipolaron stabilization by structural factors. Synth. Met. 1997;87:115-118.

[15] (2007) I. The 2007 Recommendations of ICRP. Ann. ICRP 37(2-4), ICRP Publ. 103.

[11] Yu PY, Cardona M. Fundamentals of Semiconductors. 1999. p. 617.

[13] Kittel C. Introduction to solid state physics. 5 ed. Wiley; 1976. p. 599.

versity of California, Berkeley; 1926. p. 78.

lor & Francis; 1997. p. 240.

208 Evolution of Ionizing Radiation Research

editor. Florida: CRC Press; 1984.

ids. Elsevier B.V.; 2010;356:2429-2432.

A Polym. Chem. 2006;44:4904-4915.

Chemical Society; 1994. p. 527.

Polym. J. 4:79-86.

Org. Electron. Elsevier B.V.; 2013;14:1467-1476.

Press; 1985. p. 384.

im. II. New York: Academic Press; 1966. p. 167-239.


**Industrial Application**

#### **Chapter 9**

## **Ionizing Radiations in Entomology**

Valter Arthur, Andre Machi and Thiago Mastrangelo

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/60409

#### **Abstract**

Radiation in the form of particles (α or β particles and neutrons) or electromagnetic waves (gamma or X-rays) can induce biological effects in insect cells like in other living cells. Ionization and chemical damages to organic molecules can be caused directly (mostly by particulate types of radiation) or indirectly by free radicals. Radioinduced ions and radicals, most of them coming from water radiolysis, may react with neighboring molecules to produce secondary DNA radicals or even chain reactions, particularly in lipids, and most of the significant biological effects results from damage to DNA. Currently, more than 300 species of arthropods, mostly of economic importance, have already been subjected to irradiation studies for basic research, pest control applications, and disinfestation of commodities (quarantine and phytosani‐ tary purposes). This chapter focused on insect sterilization and disinfestation by ionizing radiations in view of the socioeconomic impacts. The release of insects that are sterile after exposure to radiation aiming to control or eradicate pest populations revealed to be a revolutionary tactic in the area-wide management of pests, and many successful cases with the application of the sterile insect technique can be found around the globe. The use of ionizing radiations to inhibit the spread of quarantine insects represents an important alternative postharvest control, and the development of generic radiation treatments has resulted in a significant increase in the interna‐ tional use of phytosanitary irradiation for trade in horticultural products and other commodities

**Keywords:** Radiation, sterile insects, phytosanitary irradiation

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### **1. Introduction**

The radioentomology can be defined as a branch of science that deals with the effects of ionizing radiations over insects and the study of insects using nuclear techniques. Radioento‐ mological studies have been extremely useful in elucidating many entomological problems that were previously considered hard to solve or even insoluble due to limitations posed by conventional methods available.

The first radiobiological experiments performed with insects were initiated at the end of the 19th century. One of the first bioassays was performed by Professor Axenfelt in 1897 with house flies, but due to the methodology used, the results were not conclusive [1]. In 1911, Hunter made a series of experiments exposing several arthropods to X-rays, like *Sitophilus oryzae* L., *Culex pipiens* L., and some species of ticks, but no effects upon fertility or the tested life stages were observed. In the fall of 1912, Morgan and Runner performed experiments at Florida with the cigarette beetle *Lasioderma serricorne* F. with an X-ray machine aiming to sterilize cigar boxes in commercial scale. Their results, however, were also negative, as the beetle presented normal development.

According to Runner [2], the negative results from previous tests were caused by the fact that the equipments used were too rudimental. Most X-ray tubes that were tested were unable to operate continuously without neither fluctuation of intensity nor alteration of penetration power, being impossible to establish precisely the radiation dosage. Runner then executed new experiments with *L. serricorne*, using a device improved by W.D. Coolidge, whose X-ray tubes received a pure electron discharge, intensity and penetration power did not vary, and start and running voltages were the same. All these characteristics resulted in a homogeneous irradiation, and sterilization could be reached with high doses.

More detailed investigations on the genetic effects caused by ionizing radiations began with Muller's demonstration that genetic damage and a larger number of dominant lethal mutations could be induced in *Drosophila melanogaster* Meigen by X-rays [3]. He demonstrated, for instance, that an X-ray dose around 49 Gy applied on spermatic cells of *D. melanogaster* increased 100-fold the mutation frequency per generation.

However, entomologists became really aware of the extension of Muller's discovery only after 1950, when Muller made a great effort to publicize the biological effects of radiation. That moment of the 20th century could be considered as the rising of radioentomology.

Currently, there are almost 3000 references in literature, published continuously for the past seven decades. One of the most complete sources of information about radiation effects on the major groups of insects is the International Database on Insect Disinfestation and Sterilization (IDIDAS; http://www-ididas.iaea.org/ididas/). This website was developed with the aim to collect data of radiation doses for sterilization and disinfestations of arthropods, also per‐ forming a comparative analysis and quality assurance check on existing data [4]. IDIDAS have provided scientists a basis for literature searches to better plan experiments and became a comprehensive entry to the scientific literature for regulatory authorities to evaluate steriliza‐ tion or disinfestation methods.

Over 300 species of arthropods, mostly of economic importance, have already been subjected to irradiation studies for basic research, pest control applications, and disinfestation of commodities (quarantine and phytosanitary purposes) [4]. In addition, insects may be labeled with stable or radioactive isotopes for radioecology or feeding studies. Nevertheless, this chapter will focus on insect sterilization and disinfestation by ionizing radiations in view of the socioeconomic impacts.

#### **2. Effects of ionizing radiations in insects and radiation sources**

**1. Introduction**

214 Evolution of Ionizing Radiation Research

conventional methods available.

beetle presented normal development.

tion or disinfestation methods.

irradiation, and sterilization could be reached with high doses.

increased 100-fold the mutation frequency per generation.

The radioentomology can be defined as a branch of science that deals with the effects of ionizing radiations over insects and the study of insects using nuclear techniques. Radioento‐ mological studies have been extremely useful in elucidating many entomological problems that were previously considered hard to solve or even insoluble due to limitations posed by

The first radiobiological experiments performed with insects were initiated at the end of the 19th century. One of the first bioassays was performed by Professor Axenfelt in 1897 with house flies, but due to the methodology used, the results were not conclusive [1]. In 1911, Hunter made a series of experiments exposing several arthropods to X-rays, like *Sitophilus oryzae* L., *Culex pipiens* L., and some species of ticks, but no effects upon fertility or the tested life stages were observed. In the fall of 1912, Morgan and Runner performed experiments at Florida with the cigarette beetle *Lasioderma serricorne* F. with an X-ray machine aiming to sterilize cigar boxes in commercial scale. Their results, however, were also negative, as the

According to Runner [2], the negative results from previous tests were caused by the fact that the equipments used were too rudimental. Most X-ray tubes that were tested were unable to operate continuously without neither fluctuation of intensity nor alteration of penetration power, being impossible to establish precisely the radiation dosage. Runner then executed new experiments with *L. serricorne*, using a device improved by W.D. Coolidge, whose X-ray tubes received a pure electron discharge, intensity and penetration power did not vary, and start and running voltages were the same. All these characteristics resulted in a homogeneous

More detailed investigations on the genetic effects caused by ionizing radiations began with Muller's demonstration that genetic damage and a larger number of dominant lethal mutations could be induced in *Drosophila melanogaster* Meigen by X-rays [3]. He demonstrated, for instance, that an X-ray dose around 49 Gy applied on spermatic cells of *D. melanogaster*

However, entomologists became really aware of the extension of Muller's discovery only after 1950, when Muller made a great effort to publicize the biological effects of radiation. That

Currently, there are almost 3000 references in literature, published continuously for the past seven decades. One of the most complete sources of information about radiation effects on the major groups of insects is the International Database on Insect Disinfestation and Sterilization (IDIDAS; http://www-ididas.iaea.org/ididas/). This website was developed with the aim to collect data of radiation doses for sterilization and disinfestations of arthropods, also per‐ forming a comparative analysis and quality assurance check on existing data [4]. IDIDAS have provided scientists a basis for literature searches to better plan experiments and became a comprehensive entry to the scientific literature for regulatory authorities to evaluate steriliza‐

moment of the 20th century could be considered as the rising of radioentomology.

Ionizing radiations can be emitted in the decay process of unstable nuclei or by de-excitation of atoms in nuclear reactors, X-ray devices, cyclotrons, and other equipments. Radiation in the form of particles (α or β particles and neutrons) or electromagnetic waves (gamma or X-rays) can induce random biological effects in cells of insects likewise to other living cells [5, 6].

The chemical damage to organic molecules from the absorbing medium through which the radiation pass can be caused directly (mostly by particulate types of radiation) or indirectly by free radicals (i.e., atoms or molecules carrying at least one unpaired orbital electron in the outer shell), secondary electrons, or other charged particles [7]. The radioinduced ions and radicals, most of them coming from the water radiolysis, may react with neighboring molecules to produce secondary DNA radicals or even chain reactions, particularly in lipids. Most significant biological effects result from damage to DNA, which is the critical target in living organisms. Some radioinduced lesions in DNA are single-strand breaks in the phosphodiester linkage, double-strand breaks, base damage, protein–DNA cross-links, and protein–protein cross-links. The double-strand breaks in DNA double helix are believed to be the most important type of lesion produced in chromosome by ionizing radiation, cracking the chro‐ matin into different pieces that may result in cell killing or mutation. Examples of lethal aberrations to the cell are the dicentric and ring (which are chromosome aberrations) and the anaphase bridge (a chromatid aberration). Two relevant aberrations that are usually not lethal to the cell are symmetrical translocation and small deletions. These changes and mutations left in the genetic code will influence base pairing, coding, transcription, and gene expression [5, 7].

According to the law of Bergonie and Tribondeau, cells that are dividing are more radiosen‐ sitive. Thus, cells that have a high mitotic rate and a long mitotic future, such as the repro‐ ductive cells, stand among the most radiosensitive cells [8]. Radioinduced changes in DNA of germ cells of insects can result in physiologically compromised gametes, aspermia, infertility, and even inability to mate. Sterilization can also be a result of fragmentation in germ cell chromosomes that generated random dominant lethal mutations, translocations, deletions, and other aberrations, which will lead to the production of imbalanced gametes and early zygotic death. The later type of sterilization is explored by the sterile insect technique (SIT), a genetic control method that relies essentially on the transfer of competitive sperm from released irradiated males to wild females [9, 10].

Somatic cells are more radioresistant than germ cells since they are usually differentiated cells, which explains why lethal radiation doses must be higher than sterilizing doses [11]. In general, insects are less resistant to radiation than bacteria, protozoa, and viruses, although more radioresistant than higher vertebrates [12, 13, 14]. Dyar's rule serve to explain this difference in sensitivity to radiation, as insects have a discontinuous growth and most of the cells divide only during the molting process [15].

The radiosensitivity varies widely among and within insect orders (Figure 1) [11]. Bakri et al. [4] highlights that the comparison of radiosensitivity between insect species must clearly take into account the end result measured, like sterilization, death, or inability to reach the next life stage. Lepidopterans exhibit more resistance to be sterilized by ionizing radiation (mean sterilization doses ranging between 40 and 400 Gy) [11] because some species may present a more complex sperm transfer, spermatophore formation, lower ability for mating after irradiation, production of eupyrene and apyrene sperm, and resistance to the induction of dominant lethal mutations due to the presence of holokinetic chromosomes (diffuse centro‐ mere) [16].

Besides the inherent differences in radioresistance between species and insect orders, many other factors can influence the sensitivity to radiation. These factors can be physical or biological conditions.

The other biological conditions that can influence insect radiosensitivity are as follows:


The main physical factors that can modify insect radiosensitivity are as follows:


insects are less resistant to radiation than bacteria, protozoa, and viruses, although more radioresistant than higher vertebrates [12, 13, 14]. Dyar's rule serve to explain this difference in sensitivity to radiation, as insects have a discontinuous growth and most of the cells divide

The radiosensitivity varies widely among and within insect orders (Figure 1) [11]. Bakri et al. [4] highlights that the comparison of radiosensitivity between insect species must clearly take into account the end result measured, like sterilization, death, or inability to reach the next life stage. Lepidopterans exhibit more resistance to be sterilized by ionizing radiation (mean sterilization doses ranging between 40 and 400 Gy) [11] because some species may present a more complex sperm transfer, spermatophore formation, lower ability for mating after irradiation, production of eupyrene and apyrene sperm, and resistance to the induction of dominant lethal mutations due to the presence of holokinetic chromosomes (diffuse centro‐

Besides the inherent differences in radioresistance between species and insect orders, many other factors can influence the sensitivity to radiation. These factors can be physical or

**a.** Age/developmental stage: in general, adults are more radioresistant than pupae, which

**c.** Size and weight: large long-lived adults of some species, with higher moisture content,

**f.** Genetic differences: strains of some species adapted to diverse environments could

**c.** Irradiation dose rate: as the dose rate is lowered and the exposure time extended, more

**d.** Dose fractionation: when splitting a radiation dose in time, cells are allowed to repair

**e.** Radiation type: radiations with a higher linear energy transfer (LET), like α particles and

**e.** Diapause: diapausing larvae of some species could be more radiosensitive [20].

The main physical factors that can modify insect radiosensitivity are as follows:

The other biological conditions that can influence insect radiosensitivity are as follows:

in turn are more resistant than larvae and eggs [11].

develop different radioresistances [21].

sublethal damage can be repaired [7].

**b.** Sex: female insects are usually more radiosensitive than males [17].

may be more radiosensitive than small short-lived adults [18].

**d.** Nutritional stage: starvation may increase the radiosensitivity [19].

**a.** Atmosphere: radioinduced damages are fewer with hypoxia [22].

sublethal damage during the intervals between doses [24].

neutrons, are more effective in inducing biological effects [7].

**b.** Temperature: radioresistance may increase at lower temperatures [23].

only during the molting process [15].

216 Evolution of Ionizing Radiation Research

mere) [16].

biological conditions.

**Figure 1.** Decrease in radiosensitivity based on estimated sterilization doses for different insect orders (IDIDAS, 2015).

As aforementioned, radiations with a high LET are more effective in inducing biological effects, but their penetration can be limited. A typical alpha particle, for example, has high LET, but its penetration range is of only about 3 cm in air or 0.04 mm in tissue [7]. Neutrons also produce dense ionized tracks, but they can travel great distances in air as they carry no charge, requiring thick hydrogen-containing materials, such as concrete or water, to block them. Nevertheless, the application of neutron in radioentomological projects and pest control is constrained due to the easy induction of radioactivity in irradiated materials and the availability of neutron sources, which are usually restricted to nuclear reactors.

Researchers have preferably applied gamma or X-rays and high-energy electrons in studies involving pest control and disinfestation of commodities. As these radiations have similar relative biological effectiveness (RBE), most studies have indicated not significant differences in the biological damage induced by them for most doses and insect life stages [25, 26]. The insects are not rendered radioactive when irradiated with these sources by ensuring that the incident radiation is below 10 million electron volts (MeV) for high-energy electrons and less than 5 MeV for photons (gamma or X-rays) [27].

High-energy electrons are generated by electron accelerators, not involving any type of radioisotope. Likewise, most X-ray machines do not use radioisotopes, and X-rays are generated basically by the rapid deceleration of a beam of electrons before a material of high atomic number (e.g., tungsten or gold). The major advantages of these radiation sources are that no radioactive waste is produced, no radiation is produced when switched off, and the dose rate from electron accelerators can be hundred times greater than from gamma irradiators [11].

Despite these advantages, the types of irradiator used most frequently by radioentomologists for the past four decades have been those equipped with the radioisotopes 60Co or 137Cs as source of gamma rays. 60Co has a half-life of 5.3 years and emits two gamma photons of 1.17 and 1.33 MeV, while 137Cs has a half-life of 30.1 years and emits a monoenergetic photon of 0.66 MeV. The gamma irradiators used in pest control programs or for disinfestation of commod‐ ities are commonly of two types: large-scale panoramic irradiators or self-contained dry storage irradiators (Figure 2). The choice of radiation source is based considering basically costs, penetration, and irradiated material throughput [11]. Panoramic irradiators allow the irradiation of entire rooms and large number of samples or products can be irradiated at the same time. In self-contained irradiators, such as the most common irradiator used for insect sterilization, the Gammacell-220 (MDS Nordion International Inc., Ottawa, Canada), the canister containing the samples is lowered from the loading position to the shielded chamber with the radiation sources. The production of the Gammacell-220 was discontinued since 2008. On its place, appeared new models whose irradiation chamber contains a single source, lowering the overall costs, and the sample rotates through its own axis in front of the radiation source.

**Figure 2.** Types of gamma irradiators used in pest control trials or for disinfestation of commodities at the Center for Nuclear Energy in Agriculture (CENA, São Paulo, Brazil): (left) large-scale panoramic Gammabeam-650 irradiator; (right) self-contained Gammacell-220 irradiator.

#### **3. Sterile insect technique**

One of the main applications of ionizing radiations in Entomology is the production of sterile insects by the sterile insect technique (SIT). The SIT can be defined as a control tactic that uses area-wide inundative releases of sterile insects to reduce the fertility of a field population of the same species [28]. This technique is usually used as one of the components of area-wide integrated pest management programs, where the density of the target insect pest population is initially reduced by other control methods, like cultural or chemical control [29, 30].

Despite these advantages, the types of irradiator used most frequently by radioentomologists for the past four decades have been those equipped with the radioisotopes 60Co or 137Cs as source of gamma rays. 60Co has a half-life of 5.3 years and emits two gamma photons of 1.17 and 1.33 MeV, while 137Cs has a half-life of 30.1 years and emits a monoenergetic photon of 0.66 MeV. The gamma irradiators used in pest control programs or for disinfestation of commod‐ ities are commonly of two types: large-scale panoramic irradiators or self-contained dry storage irradiators (Figure 2). The choice of radiation source is based considering basically costs, penetration, and irradiated material throughput [11]. Panoramic irradiators allow the irradiation of entire rooms and large number of samples or products can be irradiated at the same time. In self-contained irradiators, such as the most common irradiator used for insect sterilization, the Gammacell-220 (MDS Nordion International Inc., Ottawa, Canada), the canister containing the samples is lowered from the loading position to the shielded chamber with the radiation sources. The production of the Gammacell-220 was discontinued since 2008. On its place, appeared new models whose irradiation chamber contains a single source, lowering the overall costs, and the sample rotates through its own axis in front of the radiation

**Figure 2.** Types of gamma irradiators used in pest control trials or for disinfestation of commodities at the Center for Nuclear Energy in Agriculture (CENA, São Paulo, Brazil): (left) large-scale panoramic Gammabeam-650 irradiator;

One of the main applications of ionizing radiations in Entomology is the production of sterile insects by the sterile insect technique (SIT). The SIT can be defined as a control tactic that uses

source.

218 Evolution of Ionizing Radiation Research

(right) self-contained Gammacell-220 irradiator.

**3. Sterile insect technique**

The idea of releasing insects of the same species to introduce sterility into wild populations was independently conceived on the 1930*s* by three researchers: A.S. Serebrovskii at the USSR, F.L. Vanderplank at Tanzania, and E.F. Knipling from the United States [31]. Serebrovskii used chromosomal translocations to induce inherited partial sterility in *Musca domestica* L. and *Calandra granaria* L., but his research was not continued in the USSR during World War II [32]. Vanderplank tried to use hybrid sterility to combat tsetse flies, after obtaining low fertility from cross-matings between *Glossina morsitans* Westwood and *Glossina swynnertoni* Austen, but the detailed results were not published until his death [33]. At the United States Depart‐ ment of Agriculture (USDA), Knipling and colleagues [31, 34, 35, 36] exploited Muller's discovery that ionizing radiation could induce dominant lethal mutations, and their studies continued despite the tribulations during the World War II, resulting in an approach that was applied to eradicate the New World Screwworm, *Cochliomyia hominivorax* Coquerel, from the United States and Central America.

The SIT does not apply to all insects species. Innumerous factors must be considered before the adoption of the technique: (a) the species must reproduce sexually (even low levels of parthenogenesis can derail the technique); (b) the technique can be impractical for species that are vector of serious diseases, nuisance pests, or those which are highly destructive in the adult stage; (c) mass rearing procedures must be available; (d) the released sterile insects must present adequate dispersion; (e) the sterilization must not compromise the competitiveness of the males; (f) females must preferably mate only once or irradiated sperm must be very competitive; and (g) the population density of the target pest must be low, making economi‐ cally feasible the release of a dominant population of sterile males over an extended period of time [34, 37].

Knipling et al. [38] realized that the degree of sterility introduced into the wild population by the sterile males must be sufficiently high to overcome the rate of increase of the wild females in order to provoke an overall reduction in the target population. As the ratio of sterile to fertile insects increases asymptotically as the density of the wild population declines to low levels, Knipling advocated that the sterile insects should be released when the wild population was at a seasonal low or after its decimation by weather events or other control methods. Most of the successful programs that released sterile insects were applied when field populations were at low densities [29].

Basically, the SIT involves the mass rearing of the target species, exposing the insects to ionizing radiation to induce sexual sterility, and then releasing the irradiated insects into the target population. The released sterile males mate with wild females, preventing the generation of a fertile offspring [10, 39].

The production of high quality insects in sufficient numbers using mass-rearing techniques is one of the main steps of the technique [40]. Methods to rear insects on artificial diets have been developed for more than 1000 species so far [41–45]. The production must be timely and cost effective, taking advantage of economies of scale whenever possible [46–49], and maximum attention must be paid to the factors that can affect quality of the insects produced [50].

Since the 1950s, most of the insect pest control programs that integrate the SIT have applied radioisotope irradiators loaded either with 60Co or 137Cs, sterilizing the insects, therefore, with gamma rays [11, 51, 52]. Sterilization doses for hundreds of insect species can be found at IDIDAS database [53]. As absorbed dose is a key parameter for the success of the technique, the facilities that sterilize insects must have an accurate dosimetry system [11]. Due the growing complexities of the transboundary shipment of radioisotopes and the fear of "dirty bombs" after the September 11 attacks, some studies have supported the adoption of other practical alternatives for the sterilization of insects, such as X-ray irradiators [26, 54–58].

Studies aiming to develop procedures for handling and chilling adult insects or to provide food and water prior to release are continually performed. After sterilization, the insects can be released via static-release receptacles, ground-release methods, or most commonly from the air [59]. One of the most efficient methods of release is the aerial release of chilled irradiated insects or bags containing the adults, especially when aircraft flight paths are guided by a global positioning system (GPS) linked to a computer-controlled release mechanism [59, 60].

The SIT has been used mostly against species that are highly harmful to agriculture or public health or which elimination would have significant economic benefits. Currently, about 38 facilities are making research on SIT or sterilizing millions of insects per week for national area-wide integrated pest control programs [53]. Effective programs integrating the SIT have been performed against screwworm flies, tropical fruit flies, some species of tsetse flies, the pink bollworm *Pectinophora gossypiella* Saunders, and the codling moth *Cydia pomonella* L.

One of the best examples of application of the SIT was the phenomenal successful eradication campaigns conducted against the New World Screwworm, *C. hominivorax*, in the American continent. This fly can be sterilized as pupae 24 h before adult emergence with 40 Gy [61, 62]. The economic losses to livestock caused by *C. hominivorax* in the United States during the 1930s were significant [63]. After the field pilot tests at the Sanibel Island (1951–1953) and the Curaçao Island (1954) [64], eradication campaigns using suppression techniques and sterile insects were implemented in the Southeastern (1957–1959) and Southwestern (1962–1966) United States. As fertile flies continued infesting the United States coming from Central America, the eradication campaigns advanced through Mexico. Using sterile flies reared in the mass-rearing facility from COMEXA (*Comisión México-Americana para la Erradicación del Gusano Barrenador del Ganado*) at Tuxtla Gutiérrez, Mexico, the eradication of *C. hominivorax* was achieved until the Isthmus of Tehuantepec in 1984. With the interest of Central American countries and as fewer sterile flies would be required to maintain a buffer zone at Panama (150 million sterile flies/ week were needed in the Isthmus of Tehuantepec, while only 40 million/week would be required in Panama), national eradication campaigns continued with the aerial release of more than 20 million sterile flies/week [65] during more than two decades (Figure 3). Panama was finally declared free from *C. hominivorax* in 2006 and a biological barrier of 30,000 km2 , maintained by the weekly release of 50 million sterile flies, was set at the Darien Gap [65, 66]. With this eradication effort, all warm-blooded animals became free of this deadly parasite in the United States, Mexico, Belize, Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica, Panama, some Caribbean Islands, and additionally Libya, North Africa, after an outbreak [36, 67]. The economic benefits of these campaigns trespassed US\$1 billion per year [68].

developed for more than 1000 species so far [41–45]. The production must be timely and cost effective, taking advantage of economies of scale whenever possible [46–49], and maximum attention must be paid to the factors that can affect quality of the insects produced [50].

220 Evolution of Ionizing Radiation Research

Since the 1950s, most of the insect pest control programs that integrate the SIT have applied radioisotope irradiators loaded either with 60Co or 137Cs, sterilizing the insects, therefore, with gamma rays [11, 51, 52]. Sterilization doses for hundreds of insect species can be found at IDIDAS database [53]. As absorbed dose is a key parameter for the success of the technique, the facilities that sterilize insects must have an accurate dosimetry system [11]. Due the growing complexities of the transboundary shipment of radioisotopes and the fear of "dirty bombs" after the September 11 attacks, some studies have supported the adoption of other practical alternatives for the sterilization of insects, such as X-ray irradiators [26, 54–58].

Studies aiming to develop procedures for handling and chilling adult insects or to provide food and water prior to release are continually performed. After sterilization, the insects can be released via static-release receptacles, ground-release methods, or most commonly from the air [59]. One of the most efficient methods of release is the aerial release of chilled irradiated insects or bags containing the adults, especially when aircraft flight paths are guided by a global positioning system (GPS) linked to a computer-controlled release mechanism [59, 60]. The SIT has been used mostly against species that are highly harmful to agriculture or public health or which elimination would have significant economic benefits. Currently, about 38 facilities are making research on SIT or sterilizing millions of insects per week for national area-wide integrated pest control programs [53]. Effective programs integrating the SIT have been performed against screwworm flies, tropical fruit flies, some species of tsetse flies, the pink bollworm *Pectinophora gossypiella* Saunders, and the codling moth *Cydia pomonella* L.

One of the best examples of application of the SIT was the phenomenal successful eradication campaigns conducted against the New World Screwworm, *C. hominivorax*, in the American continent. This fly can be sterilized as pupae 24 h before adult emergence with 40 Gy [61, 62]. The economic losses to livestock caused by *C. hominivorax* in the United States during the 1930s were significant [63]. After the field pilot tests at the Sanibel Island (1951–1953) and the Curaçao Island (1954) [64], eradication campaigns using suppression techniques and sterile insects were implemented in the Southeastern (1957–1959) and Southwestern (1962–1966) United States. As fertile flies continued infesting the United States coming from Central America, the eradication campaigns advanced through Mexico. Using sterile flies reared in the mass-rearing facility from COMEXA (*Comisión México-Americana para la Erradicación del Gusano Barrenador del Ganado*) at Tuxtla Gutiérrez, Mexico, the eradication of *C. hominivorax* was achieved until the Isthmus of Tehuantepec in 1984. With the interest of Central American countries and as fewer sterile flies would be required to maintain a buffer zone at Panama (150 million sterile flies/ week were needed in the Isthmus of Tehuantepec, while only 40 million/week would be required in Panama), national eradication campaigns continued with the aerial release of more than 20 million sterile flies/week [65] during more than two decades (Figure 3). Panama was finally declared free from *C. hominivorax* in 2006 and a biological barrier of 30,000 km2

maintained by the weekly release of 50 million sterile flies, was set at the Darien Gap [65, 66]. With this eradication effort, all warm-blooded animals became free of this deadly parasite in

,

**Figure 3.** Expansion of the eradication campaigns that used aerial releases of irradiated flies against the New World Screwworm in North and Central America.

Many species of fruit flies are major economic pests due to the direct and indirect damages caused to fruit growers and difficulties imposed to international trade of fruits and vegetables [69]. Because of that, some species, especially tephritid fruit flies, have been target of programs that integrate the SIT. Fruit flies from the Tephritidae family can be generally sterilized at 90– 150 Gy, and *Bactrocera* spp. are usually sterilized at 30–90 Gy [11, 53]. The first large-scale program stopped the invasion of the Mediterranean fruit fly (medfly) *Ceratitis capitata* Wiedemann from Central America into southern Mexico in the 1970s [70, 71]. After the invasion of Costa Rica by the medfly in 1955 and its expansion up to southern Mexico in 1976, the Government of Mexico started working with Guatemala and the United States to establish a large area-wide program using the SIT against this pest [71]. Using 500 million sterile flies/ week from the rearing facility at Metapa, Mexico, and, currently, almost 2 billion sterile males/ week [69, 72] from the biofactory located at El Piño, Guatemala, the MOSCAMED program has kept the United States, Mexico, and half of Guatemala free of the medfly for over 35 years. To prevent the establishment of the medfly in the continental United States through infested imported fruits, sterile males are regularly released in the Los Angeles Basin and Florida [31, 73]. During the 1980s and 1990s, the SIT was employed to eradicate the melon fly *Bactrocera cucurbitae* Coquillett in all of Japan's southwestern islands [74]. Significant SIT programs against the medfly and *Anastrepha* species have also been developed in several provinces of Argentina, some of which have become pest-free areas [75, 76].

Sterilization doses for flies from the Glossinidae family range from 50 to 120 Gy [53], and some SIT trials have been conducted on tsetse flies, which are vectors of trypanosomosis ("sleeping sickness"), in African countries during the 1970s and 1980s. However, as most programs had not been conducted area-wide, the pest-free status of most of the areas could not be maintained [31]. For example, three tsetse species (*G. morsitans submorsitans* Newstead, *Glossina palpalis gambiensis* Vanderplank, *G. palpalis palpalis* Robineau-Desvoidy) were eradicated at the same time in 3,000 km2 from Burkina Faso through insecticide application and trapping suppression, followed by ground release of irradiated adults [77]. *G. palpalis palpalis* was eradicated in 1,500 km2 of Nigeria with traps and insecticide-impregnated targets followed by ground releases of sterile adults [78]. In 1994–1997, *Glossina austeni* Newstead was eradicated from Unguja Island of Zanzibar (1,650 km2 ) by using attractive devices, treating livestock with insecticide and aerial releases of irradiated adults, ceasing the transmission of trypanosomosis [79, 80]. The government of Ethiopia started the Southern Tsetse Eradication Project (STEP) in 2009, aiming to eradicate two species of tsetse flies over a 25,000 km2 area in the Southern Rift Valley [81, 82], and after area-wide suppression activities, the mass-rearing facility in the Kality suburb of Addis Ababa had supplied in 2012 up to 60,000 sterile males/week to be released over the Deme Basin region. Since 2012, very good progress is also being made in the eradication of *G. palpalis gambiensis* on the Niayes area in Senegal with aerial releases of sterile males [60], and the annual increases of cattle sales after eradication were estimated in more than € 2,800/km2 for the farming communities.

Despite some difficulties when applying the SIT against moths [83], like high mean sterilization doses (usually higher than 100 Gy) and appropriate air-handling and filtering in the massrearing facilities, radiobiological studies have been conducted for more than 30 lepidopteran species [84] and two SIT programs are still operational.

Since 1968, the pink bollworm, *Pectinophora gossypiella* Saunders, has been excluded from the San Joaquin Valley, USA, by a containment program [85] (http://www.cotton.org/tech/pest/ bollworm/index.cfm), which releases adults that emerge from pupae irradiated with 100–150 Gy at the rearing facility in Phoenix, Arizona. The cost of this program has been around US \$12.5/ha/season for each cotton grower (but control costs would increase by US\$200/ha per grower if the program was not in place, besides an additional 2.2 million kg of pesticide that would have to be used every year) [83].

Populations of the codling moth, *Cydia pomonella* L., from British Columbia are being kept at insignificant levels since 1997 and individuals of this pest have not been detected in 37% of the orchards since 2009 due to the Okanagan-Kootenay suppression program that integrates the SIT (newly emerged males are partially sterilized with 100–250 Gy and chilled moths are released). Growers used to pay a tax of US\$169/ha/year, and the application of insecticides in the province was reduced 82% since then [83, 86, 87].

#### **4. Radiation as quarantine treatment against insect pests**

imported fruits, sterile males are regularly released in the Los Angeles Basin and Florida [31, 73]. During the 1980s and 1990s, the SIT was employed to eradicate the melon fly *Bactrocera cucurbitae* Coquillett in all of Japan's southwestern islands [74]. Significant SIT programs against the medfly and *Anastrepha* species have also been developed in several provinces of

Sterilization doses for flies from the Glossinidae family range from 50 to 120 Gy [53], and some SIT trials have been conducted on tsetse flies, which are vectors of trypanosomosis ("sleeping sickness"), in African countries during the 1970s and 1980s. However, as most programs had not been conducted area-wide, the pest-free status of most of the areas could not be maintained [31]. For example, three tsetse species (*G. morsitans submorsitans* Newstead, *Glossina palpalis gambiensis* Vanderplank, *G. palpalis palpalis* Robineau-Desvoidy) were eradicated at the same

followed by ground release of irradiated adults [77]. *G. palpalis palpalis* was eradicated in 1,500 km2 of Nigeria with traps and insecticide-impregnated targets followed by ground releases of sterile adults [78]. In 1994–1997, *Glossina austeni* Newstead was eradicated from Unguja Island

aerial releases of irradiated adults, ceasing the transmission of trypanosomosis [79, 80]. The government of Ethiopia started the Southern Tsetse Eradication Project (STEP) in 2009, aiming

82], and after area-wide suppression activities, the mass-rearing facility in the Kality suburb of Addis Ababa had supplied in 2012 up to 60,000 sterile males/week to be released over the Deme Basin region. Since 2012, very good progress is also being made in the eradication of *G. palpalis gambiensis* on the Niayes area in Senegal with aerial releases of sterile males [60], and the annual increases of cattle sales after eradication were estimated in more than € 2,800/km2

Despite some difficulties when applying the SIT against moths [83], like high mean sterilization doses (usually higher than 100 Gy) and appropriate air-handling and filtering in the massrearing facilities, radiobiological studies have been conducted for more than 30 lepidopteran

Since 1968, the pink bollworm, *Pectinophora gossypiella* Saunders, has been excluded from the San Joaquin Valley, USA, by a containment program [85] (http://www.cotton.org/tech/pest/ bollworm/index.cfm), which releases adults that emerge from pupae irradiated with 100–150 Gy at the rearing facility in Phoenix, Arizona. The cost of this program has been around US \$12.5/ha/season for each cotton grower (but control costs would increase by US\$200/ha per grower if the program was not in place, besides an additional 2.2 million kg of pesticide that

Populations of the codling moth, *Cydia pomonella* L., from British Columbia are being kept at insignificant levels since 1997 and individuals of this pest have not been detected in 37% of the orchards since 2009 due to the Okanagan-Kootenay suppression program that integrates the SIT (newly emerged males are partially sterilized with 100–250 Gy and chilled moths are released). Growers used to pay a tax of US\$169/ha/year, and the application of insecticides in

from Burkina Faso through insecticide application and trapping suppression,

) by using attractive devices, treating livestock with insecticide and

area in the Southern Rift Valley [81,

Argentina, some of which have become pest-free areas [75, 76].

to eradicate two species of tsetse flies over a 25,000 km2

species [84] and two SIT programs are still operational.

the province was reduced 82% since then [83, 86, 87].

would have to be used every year) [83].

time in 3,000 km2

of Zanzibar (1,650 km2

222 Evolution of Ionizing Radiation Research

for the farming communities.

One major concern in exporting agricultural commodities is to prevent the introduction or spread of exotic quarantine pests. Phytosanitary measures are used to disinfest commodities of pests, providing quarantine security [88]. The fumigant gas methyl bromide used to be the most common treatment for agricultural commodities [89] due the low cost, effectiveness against a wide range of insects, rapid dispersion, and minimal impact on commodity quality [90]. However, with the imminent phasing out of methyl bromide as mandated by the Montreal Protocol [91], the interest in alternative phytosanitary treatments has raised [92, 93]. The use of ionizing radiations as a way to inhibit the spread of quarantine insects represents an important alternative postharvest control, reducing the need for chemical fumigants and other toxic products [94].

Hallman [95] stated that the objective of using ionizing radiations as a phytosanitary treatment is not to obtain acute mortality of the insects but to prevent development or reproduction, as most commodities do not tolerate the usual dose ranges required to achieve immediate mortality (usually ≥1 kGy). Actually, the U.S. Food and Drug Administration (FDA) has approved radiation up to 1 kGy to control insects in foods and to extend the shelf life of fresh fruits and vegetables [96]. Thus, a phytosanitary irradiation treatment must be effective against the most tolerant insect stage that could be present on the commodity [97], and the inhibition of further development should be considered as a measure of efficacy of phytosanitary irradiation [98].

Some regulators may consider this a disadvantage since other commercially applied quaran‐ tine treatments, which are generally based on heat, cold or methyl bromide fumigation, do reach acute mortality. When inspectors find live quarantine pests from these treatments, the entire consignment can be rejected or retreated regardless of certification of treatment because the inspectors may assume that the treatment was not properly done, the shipment was contaminated with infested commodity or the cargo was reinfested after treatment. Further‐ more, live adults found in survey traps could trigger restrictive and costly regulatory responses in importing countries [99].

Nevertheless, phytosanitary irradiation can be a viable commercial insect control technique. The advantages of radiation include the fact that pest insects cannot develop resistance, the absence of residual radioactivity, and few significant changes in the physicochemical proper‐ ties of the treated products for most doses applied [100].

Another advantage of phytosanitary irradiation compared with other treatments is the possibility of using generic doses (i.e., one dose serves for a group of insects and commodities, although not all have been tested for efficacy), which facilitate the development and applica‐ tion of the treatment [94].

Radioentomologists are constantly looking for a generic radiation dose to serve as quarantine treatment, i.e. a dose that could control a broad group of pests without adversely affecting the quality of a wide range of commodities [101]. This dose would necessarily be set at the minimum absorbed dose required for the most tolerant organism within the insect group considered [102]. Due the high radiotolerance of the Angoumois grain moth (*Sitotroga cerealella* Olivier), Hallman and Phillips [102] suggested that a generic dose of 600 Gy for all insects in ambient atmospheres would be efficacious to attend quarantine purposes. Currently, some of the generic phytosanitary irradiation treatments are 150 Gy for all hosts of Tephritidae, 150 Gy also for mangoes and citrus fruits exported from Mexico to the United States, 250 Gy for all arthropods on mango and papaya shipped from Australia to New Zealand [103], 300 Gy for all arthropods on mango shipped from Australia to Malaysia, 350 Gy for all arthropods on lychee shipped from Australia to New Zealand, and 400 Gy is applied for Mexican guavas, Indian mangoes, and dragon fruit (*Hylocereus undatus* Britton and Rose) from Vietnam exported to the United States [94, 99]. Hallman [88] also presented a number of cases indicating the usefulness of generic doses for important pest groups such as mealybugs, scales, and weevils.

In 2006, the USDA approved irradiation at a generic dose of 150 Gy for any tephritid fruit fly and 400 Gy for all insects except pupae and adult of Lepidoptera [88, 104, 105]. Subsequent studies lead the USDA-APHIS to approve minimum doses for 23 insect pests [106], including 10 tephritid fruit fly species, 6 lepidopteran species, 4 curculionid species, and 1 mite species. These approved specific doses for fruit flies range between 60 and 150 Gy, between 100 and 250 Gy for lepidopterans, between 92 and 300 Gy for Coleoptera, and 300 Gy for the spider mite [106].

The International Plant Protection Convention (IPPC) also accepted the 150 Gy minimum absorbed dose for Tephritids as an international standard for phytosanitary treatment of these quarantine pests, including it in the International Standards of Phytosanitary Measures (ISPM #28) together with 13 species-specific treatment procedures [107]. The IPPC, however, did not accept the generic dose of 400 Gy for all insects (except pupae and adult of lepidopterans). The IPPC does not approve at first some irradiation treatments due to perceived problems with the study or the presence of live adults after irradiation (an issue that must be carefully addressed).

The development of methods to determine whether quarantine pests have been irradiated could help to resolve the issue of presence of live adults after exposure to radiation. Biomarkers based on the molecular processes of irradiation-induced DNA damage and repair would have internationally broad application to confirm the irradiation status of pests found on commod‐ ities and for the detection of sterile insects. Siddiqui et al. [108] discovered a protein in the Queensland fruit fly, *Bactrocera tryoni* Froggatt, that was modified due to radiation, with a higher amount of modified protein at higher radiation doses. The authors also tested the doses approved for disinfestation and SIT. Leifert et al. [109] reported highly specific antibodies that allowed the sensitive detection of proteins from irradiated *B. tryoni* using even standard commercial technologies, such as western blot or ELISA assays.

According to Follett [110], current research on phytosanitary irradiation is focused on devel‐ opment of specific doses for quarantine lepidopterans not covered by the generic treatments, shortening treatment time through the reduction of dose levels for specific pests and com‐ modities, the development of generic doses below 400 Gy for economically important groups of quarantine insects other than fruit flies, and deep investigations on commodity tolerance and novel methods to reduce damages and extend shelf life. The author also discussed that future research should be dedicated to reduce the present barriers to the wider use of phyto‐ sanitary irradiation, like the 1 kGy limit, restrictions on the use of modified atmosphere and the small number of countries that approve the use of phytosanitary irradiation. For example, the development of small-scale X-ray machines could provide farmers and packinghouses with in-house treatment capability, accelerating the adoption of phytosanitary irradiation. A recent change in U.S. import regulations has permitted the irradiation upon entry, allowing exporting countries to explore new markets without investing in expensive irradiation facilities [111].

#### **5. Conclusion**

considered [102]. Due the high radiotolerance of the Angoumois grain moth (*Sitotroga cerealella* Olivier), Hallman and Phillips [102] suggested that a generic dose of 600 Gy for all insects in ambient atmospheres would be efficacious to attend quarantine purposes. Currently, some of the generic phytosanitary irradiation treatments are 150 Gy for all hosts of Tephritidae, 150 Gy also for mangoes and citrus fruits exported from Mexico to the United States, 250 Gy for all arthropods on mango and papaya shipped from Australia to New Zealand [103], 300 Gy for all arthropods on mango shipped from Australia to Malaysia, 350 Gy for all arthropods on lychee shipped from Australia to New Zealand, and 400 Gy is applied for Mexican guavas, Indian mangoes, and dragon fruit (*Hylocereus undatus* Britton and Rose) from Vietnam exported to the United States [94, 99]. Hallman [88] also presented a number of cases indicating the usefulness of generic doses for important pest groups such as mealybugs, scales, and

In 2006, the USDA approved irradiation at a generic dose of 150 Gy for any tephritid fruit fly and 400 Gy for all insects except pupae and adult of Lepidoptera [88, 104, 105]. Subsequent studies lead the USDA-APHIS to approve minimum doses for 23 insect pests [106], including 10 tephritid fruit fly species, 6 lepidopteran species, 4 curculionid species, and 1 mite species. These approved specific doses for fruit flies range between 60 and 150 Gy, between 100 and 250 Gy for lepidopterans, between 92 and 300 Gy for Coleoptera, and 300 Gy for the spider

The International Plant Protection Convention (IPPC) also accepted the 150 Gy minimum absorbed dose for Tephritids as an international standard for phytosanitary treatment of these quarantine pests, including it in the International Standards of Phytosanitary Measures (ISPM #28) together with 13 species-specific treatment procedures [107]. The IPPC, however, did not accept the generic dose of 400 Gy for all insects (except pupae and adult of lepidopterans). The IPPC does not approve at first some irradiation treatments due to perceived problems with the study or the presence of live adults after irradiation (an issue that must be carefully

The development of methods to determine whether quarantine pests have been irradiated could help to resolve the issue of presence of live adults after exposure to radiation. Biomarkers based on the molecular processes of irradiation-induced DNA damage and repair would have internationally broad application to confirm the irradiation status of pests found on commod‐ ities and for the detection of sterile insects. Siddiqui et al. [108] discovered a protein in the Queensland fruit fly, *Bactrocera tryoni* Froggatt, that was modified due to radiation, with a higher amount of modified protein at higher radiation doses. The authors also tested the doses approved for disinfestation and SIT. Leifert et al. [109] reported highly specific antibodies that allowed the sensitive detection of proteins from irradiated *B. tryoni* using even standard

According to Follett [110], current research on phytosanitary irradiation is focused on devel‐ opment of specific doses for quarantine lepidopterans not covered by the generic treatments, shortening treatment time through the reduction of dose levels for specific pests and com‐ modities, the development of generic doses below 400 Gy for economically important groups of quarantine insects other than fruit flies, and deep investigations on commodity tolerance

commercial technologies, such as western blot or ELISA assays.

weevils.

224 Evolution of Ionizing Radiation Research

mite [106].

addressed).

The use of ionizing radiations allowed the rise of a new branch of the study of insects in the middle of the 20th century, the radioentomology. The release of insects that are sterile after exposure to radiation aiming to control or eradicate pest populations revealed to be a revolu‐ tionary tactic in the area-wide management of pests, and many successful cases of the application of the sterile insect technique can be found around the globe. Furthermore, the development of generic radiation treatments has resulted in a significant increase in the international use of phytosanitary irradiation for trade in horticultural products and other commodities.

#### **Author details**

Valter Arthur, Andre Machi and Thiago Mastrangelo\*

\*Address all correspondence to: thiagomastrangelo@gmail.com

Center for Nuclear Energy in Agriculture (CENA/USP), Brazil

#### **References**


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