**6. The proton radiography**

*Applications of Optical Fibers for Sensing*

maximum value.

per second.

TIFPA, is shown.

**5. Beam profile measurement**

from the entrance window where the intensity of the signal is one tenth of its

This distance corresponds to the layer on the right of the Bragg peak (or the next layer compared to the incident beam direction). The results of this measurement are compared with the range values calculated by means of a Monte Carlo simulation of the response of the detector. Both data sets were fitted with the power law (Eq. (1)):

*R* = *a* + *b* ⋅ *E*1.75 (1)

where *R* is the range of the protons in the RRD, *E* is the kinetic energy at the

The same measurement was performed at TIFPA with proton energy in the

conditions. It is able to measure the size and the position of the beam spot. As a

In order to extend the range of the RRD, a series of calibrated water-equivalent range shifters, 10-mm-thick polystyrene slab phantoms was placed in front of the entry window of the RRD every time the energy of the beam exceeded the range of detector alone. In **Figure 7**, the range vs. energy calibration graph, measured at

protons

particles per second therapy

range between 70 and 250 MeV and with a high-intensity beam, up to 109

entrance of the RRD, and *a* and *b* are free parameters of fit.

The PSD can work as a profilometer at rate up to 109

**88**

**Figure 8.**

*to data.*

*Examples of Y profile of the proton beam spot at 70 MeV. The calculated Gaussian fit, in red, is superimposed* 

The PSD and RRD have been tested in radiography configuration at CATANA. In this test, the experimental setup is the one previously described, but the two detectors were simultaneously active.

In order to acquire a radiographic image, a range measurement must be performed for each particle crossing the PSD at a given position. Then, data acquisition must run at low beam intensity (imaging conditions, about 106 particles per second on average). When a particle causes a quadruple time coincidence in the PSD, the crossing position within the sensitive area is measured, and a trigger signal starts the measurement of the particle range in the RRD. The software analysis associates the positions measured by the PSD to the RRD range measurements event by event. At the end of data acquisition for each pixel, the software analysis calculates the centroid by Gaussian fit of the range measurements distribution corresponding to that pixel. The result of this analysis is, therefore, a 160 **×** 160 matrix, as many as the PSD pixels, in which each element is the centroid of the range measurement of the particles that have crossed the corresponding pixel. Note that the use of a single PSD placed before the RRD can introduce a not negligible error for the fact that the input and output particle crossing positions through the calibrated target one must necessarily be assumed coincident or

**Figure 9.** *The radiography of the ladder target with A12 range shifter.*

undergone a negligible deflection traversing the medium. This error could be minimized using multiple PSD at different depths in the RRD.

A simple PVC target with the shape of a ladder was designed for the radiography test. Due to the homogeneous density of the target, in the radiography, only the differences in thickness traversed by the protons can be distinguished. The radiography image reported in **Figure 9** refers to a 3.5 cm diameter beam crossing a PMMA range shifter of about 10 mm thickness.

The z value in **Figure 9** is the centroid of the range distribution, expressed in numbers of RRD layers, pixel by pixel. Notice that the empty quarter-circle sector refers to the thickest step, 15 mm thick, of the ladder. The 58 MeV protons of the CATANA beam have insufficient energy to exit after passing through the thickness of the A12 range shifter and 15 mm of PVC. Moreover, border effects due to the nonorthogonality of the ladder with respect to the beam axis and the unavoidable divergence of the beam caused by the use of range shifters are visible in the radiography. The void pixels within the spot correspond to pixels where the range measurement statistics is too low. Many of these pixels are aligned along the same row or column, suggesting a correlation to low efficiency of the tracker in those areas. Two different 3D perspectives of the radiography are shown in **Figure 10(a)** and **(b)**. The last step in the analysis is the calculation of the relation between the measured range and the ΔE energy lost by the particles. The ΔE calculation must also take into account the energy lost by the particles in the PSD, which is placed between the target and the RRD. Since the sensitive areas of both detectors consist of 500 μm layers of SciFi, the PSD can be considered as an extension of the RRD. The residual proton range in the PSD and RRD was simulated as a function of the particle initial energy in the tracker E.

The range values thus obtained were fitted to the power law reported below in the equation, where R is the particle range in the RRD and PSD, expressed as the number of layers, and the resulting fit parameters are A = −0.191 ± 0.311 and B = 0.0370 ± 0.0006 (R - square = 0.998). Therefore, the energy loss ΔE can be easily calculated as

$$\Delta E \text{[MeV]} = \text{"58 - } \left(\frac{R - A}{B}\right)^{1/1.75}$$

The final radiography obtained after applying the energy-range conversion formula is shown in **Figure 11**.

### **Figure 10.**

*Two different perspectives of the 3D representation of the radiography: (a) lateral view and (b) isometric perspective.*

**91**

*Real-Time Particle Radiography by Means of Scintillating Fibers Tracker and Residual Range…*

As mentioned earlier, radiography images reconstructed from range measurements are subject to some limitations: (i) lack of knowledge of the effective paths of the particles crossing the phantom because only one PSD was used. In this case, particle trajectories cannot be corrected according to the effect of Multiple Coulomb; (ii) further beam divergence was introduced by the tolerances in the alignment of the target, not exactly placed at isocenter and perpendicular to the incident beam direction. The reduction of the error in the calculus of the target thickness is obtained by the data filtering of range measurements. From the simulations, protons with an initial energy of 58 MeV crossing A12 range shifter, the target and the tracker, and stopping in the RRD have a maximum range straggling of σstr = 0.4 mm, which already includes the effects of initial energy spread (0.3 MeV). So, in a region of interest (ROI) corresponding to a homogeneous quarter of the target, a range of measurements around the expected value from the simulation can

Subtracting the square of the maximum range straggling value of σstr = 0.4 mm from the standard deviation of range measurements, it is again possible to find the a priori range resolution of about 170 μm. These mean range values can be converted

The combined use of a pencil beam facility and the radiographic system, presented in this chapter, could allow the development of a faster real-time

be selected plus or minus two layers (equal to six times σstr).

*The radiography of the ladder with A12 range shifter expressed in energy loss.*

into proton energy loss and subsequently into energy loss.

*DOI: http://dx.doi.org/10.5772/intechopen.81784*

**7. Radiograph data analysis**

**Figure 11.**

**8. Future developments**

*Real-Time Particle Radiography by Means of Scintillating Fibers Tracker and Residual Range… DOI: http://dx.doi.org/10.5772/intechopen.81784*

**Figure 11.** *The radiography of the ladder with A12 range shifter expressed in energy loss.*
