**1. Introduction**

Hadron therapy is a promising alternative in treatment of tumors, because it is one of the most effective techniques of external radiation therapy, which allows killing tumor cells while leaving almost intact the surrounding issue. In order to achieve the maximum effectiveness, high precision is needed in dose delivery, which requires a real-time adequate quality control of the beam parameters (position, profile, fluence, energy) combined with the precise measurement of patient positioning [1, 2]. QBeRT is a particle tracking system [3] and consists of a position-sensitive detector (PSD) and a residual range detector (RRD) (see **Figure 1**). The main parts of this system are detectors expressly designed to achieve high-resolution imaging, high-resolution residual range measurement, large sensitive area, and high-rate beam compliance. The QBeRT system performs all these tasks and, advantageously, requires a low number of readout channels, making possible the reduction of the complexity and cost of the electronic data acquisition (DAQ ) chain, by means of a readout channel reduction system patented by Istituto Nazionale di Fisica Nucleare (INFN) [4]. Both detectors, PSD and RRD, are able to work in imaging conditions, with particle rate up to 106 particles per second, and in therapy conditions (up to 109 particles per second). In imaging condition, the system is capable to realize a particle radiography and permits a real-time monitoring of the patient position in treatment room. In therapy condition, the PSD acts as a profilometer, detecting the position, the profiles, and the fluence of the beam. The combined use of the information measured by the PSD and the RRD allows to check the treatment plan in real time. The design of both detectors is based on scintillating optical fibers (SciFi) with 500 μm nominal square section.

The working principle of the scintillating optical fibers is schematized in **Figure 2**. SciFi consist of a polystyrene-based core and a PMMA cladding. The scintillating core is a mix of polystyrene and fluorescent dopants selected to produce the scintillation light when a particle releases energy in it and sets the optical characteristics for light propagation in the fiber. Scintillation light is produced isotropically but only a portion of these photons, in the two opposite directions along the fiber, can propagate by total internal reflection (TIR) mechanism. Multi-clad fibers have a second layer of cladding that has an even lower refractive index and permits TIR at a second boundary. External EMA is an optional external layer used to eliminate optical cross talk. SciFi sizes range from 0.25 to 5 mm square or round cross-sections and available in canes, spools, ribbons, and arrays.

The scintillation light is routed by the SciFi in the PSD, by means of wavelengthshifting fibers in the RRD, toward two silicon photomultiplier (SiPM) arrays, which output a proportional electric signal. PSD and RRD employ a DAQ chain divided in two sections. The first section consists of the front-end (FE) boards, which process the electric signal from the light sensor and perform the analog-to-digital conversion.

Data from the FE is acquired by a readout (RO) board based on a National Instrument system on module (SoM) for pre-analysis and filtering. The actual readout channel reduction scheme applied to the PSD limits the performances of

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

the detector when the beam spot size exceeds about 2 cm. Notice that the choice of the suitable readout channel reduction scheme and the modularity of the detector architecture allows to resize the sensitive area and the maximum beam spot size in order to fit any specific requirement. It is possible to obtain a large area detector (up

range resolution (up to 150 and 170 μm, respectively). The detectors described in this chapter have been intensively tested in imaging and therapy (up to 109

conditions [5] thanks to the collaboration with the colleagues working at CATANA facility (Centro di AdroTerapia ed Applicazioni Nucleari Avanzate at Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare in Catania), at TIFPA (Trento Institute for Fundamentals Physics Applications) in Trieste, and at CNAO (Centro

bons, layers of pre-aligned BCF-12 SCIFI, manufactured by Saint-Gobain Crystals, juxtaposed and orthogonally oriented, named the X and Y planes. The SciFi have 500 μm nominal square section. In detail, each single layer is composed of four ribbons of 40 fibers. The ribbons are optically isolated from each other by means of 220-μm-thick black adhesive tape to reduce cross talk between adjacent and overlapped ribbons. Each fiber is coated with white extra mural absorber (EMA) [6] to further reduce the cross talk between individual fibers. Particles intersecting the PSD's sensitive area deposit energy in the fibers which is partially converted in scintillation light. A fraction of this light is channeled in the core and propagated in the fiber toward the photo-sensor. When a particle loses suitable energy in all four SciFi layers, the coordinates of the intersection of its trajectory and the sensitive area

The PSD has 640 optical channels (four layers of 160 fibers each). The channel reduction system reduces the number of the readout channels without any data loss or degradation in the position measurement. The readout is performed in time coincidence, strongly reducing the effect of noise and chance coincidences, enhancing at the same time the performances of the system. The working principle of channel

) covering a range up to 250 MeV protons with high spatial and

proton/s)

, which is made of two rib-

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

to 400 *×* 400 mm2

*Working principle of the scintillating fibers.*

**Figure 2.**

Nazionale di Adroterapia Oncologica) in Pavia.

The PSD prototype has a sensitive area of 90 **×** 90 mm2

can be measured. A picture of PSD detector is shown in **Figure 3**.

**2. The position-sensitive detector**

**Figure 1.**

*Schematic of the QBeRT proton tracking system.*

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

*Applications of Optical Fibers for Sensing*

with particle rate up to 106

500 μm nominal square section.

and available in canes, spools, ribbons, and arrays.

109

detector (PSD) and a residual range detector (RRD) (see **Figure 1**). The main parts of this system are detectors expressly designed to achieve high-resolution imaging, high-resolution residual range measurement, large sensitive area, and high-rate beam compliance. The QBeRT system performs all these tasks and, advantageously, requires a low number of readout channels, making possible the reduction of the complexity and cost of the electronic data acquisition (DAQ ) chain, by means of a readout channel reduction system patented by Istituto Nazionale di Fisica Nucleare (INFN) [4]. Both detectors, PSD and RRD, are able to work in imaging conditions,

 particles per second). In imaging condition, the system is capable to realize a particle radiography and permits a real-time monitoring of the patient position in treatment room. In therapy condition, the PSD acts as a profilometer, detecting the position, the profiles, and the fluence of the beam. The combined use of the information measured by the PSD and the RRD allows to check the treatment plan in real time. The design of both detectors is based on scintillating optical fibers (SciFi) with

The working principle of the scintillating optical fibers is schematized in **Figure 2**. SciFi consist of a polystyrene-based core and a PMMA cladding. The scintillating core is a mix of polystyrene and fluorescent dopants selected to produce the scintillation light when a particle releases energy in it and sets the optical characteristics for light propagation in the fiber. Scintillation light is produced isotropically but only a portion of these photons, in the two opposite directions along the fiber, can propagate by total internal reflection (TIR) mechanism. Multi-clad fibers have a second layer of cladding that has an even lower refractive index and permits TIR at a second boundary. External EMA is an optional external layer used to eliminate optical cross talk. SciFi sizes range from 0.25 to 5 mm square or round cross-sections

The scintillation light is routed by the SciFi in the PSD, by means of wavelengthshifting fibers in the RRD, toward two silicon photomultiplier (SiPM) arrays, which output a proportional electric signal. PSD and RRD employ a DAQ chain divided in two sections. The first section consists of the front-end (FE) boards, which process the electric signal from the light sensor and perform the analog-to-digital conversion. Data from the FE is acquired by a readout (RO) board based on a National Instrument system on module (SoM) for pre-analysis and filtering. The actual readout channel reduction scheme applied to the PSD limits the performances of

particles per second, and in therapy conditions (up to

**82**

**Figure 1.**

*Schematic of the QBeRT proton tracking system.*

the detector when the beam spot size exceeds about 2 cm. Notice that the choice of the suitable readout channel reduction scheme and the modularity of the detector architecture allows to resize the sensitive area and the maximum beam spot size in order to fit any specific requirement. It is possible to obtain a large area detector (up to 400 *×* 400 mm2 ) covering a range up to 250 MeV protons with high spatial and range resolution (up to 150 and 170 μm, respectively). The detectors described in this chapter have been intensively tested in imaging and therapy (up to 109 proton/s) conditions [5] thanks to the collaboration with the colleagues working at CATANA facility (Centro di AdroTerapia ed Applicazioni Nucleari Avanzate at Laboratori Nazionali del Sud-Istituto Nazionale di Fisica Nucleare in Catania), at TIFPA (Trento Institute for Fundamentals Physics Applications) in Trieste, and at CNAO (Centro Nazionale di Adroterapia Oncologica) in Pavia.
