**4. Experimental results**

*Applications of Optical Fibers for Sensing*

*layer. (c) View of the sensitive area of the RRD.*

means of 100 μm black adhesive film. The SciFi used in the RRD are not coated with EMA because cross talk between adjacent fibers in the same layer does not affect detector resolution. The scintillation light produced in each layer at the passage of the particle is partially absorbed, reemitted, and channeled by the WLS. The two WLS coupled to a layer transfer the collected light to a channel of a SiPM array. The FE output is, then, processed by the DAQ chain. The SiPM array and the DAQ chain

*(a) View of the RRD prototype. (b) Detail of the optical coupling between SciFi and WLS fibers in a RRD* 

A charged particle crossing the RRD passes through a number of layers as a function of its initial energy, before stopping. The dose deposited in each layer increases with depth up to the Bragg peak, where the particles produce the maximum amount of scintillation light. This point corresponds approximately to the end of the particles' path in the detector, so, by detecting the layer in which the light signal is the more intense, it is possible to measure their range. The RRD's working principle is reported in **Figure 6**. A calibration of the detector allows to obtain a

*Working principle of the RRD. In this figure, the height of the yellow column is proportional to the energy* 

are identical to those used in the PSD described in the previous section.

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**Figure 6.**

**Figure 5.**

*released in each layer by a particle crossing the RRD.*

Measurements at CATANA were carried out to fully characterize the performance of the prototypes, with protons up to 58 MeV at the output in treatment room. During the last year, other measurements have taken place at TIFPA proton irradiation facility. The spatial resolution of the PSD was measured by means of a calibrated brass collimator applied at the beam pipe exit in the treatment room at CATANA. After data analysis, it is possible to estimate the holes' centers and compare them with the projection of the collimator holes on the detector plane. Then, the mean distances between the reconstructed centers and the collimator hole centers were calculated for each hole, and the mean distance was about 130 μm, comparable with the (a priori) spatial resolution of the PSD, given by 500 μm/√12. The maximum spatial resolution is an intrinsic characteristic of the detector, independent of the readout strategy.

In order to calibrate the RRD, several measures of the range have been acquired changing the initial energy of protons. At CATANA facility, the proton beam energy can be passively modulated by placing a different calibrated PMMA range shifter at the beam pipe exit. The energy of the protons at the beam pipe exit was calculated by means of Monte Carlo simulation. The Bragg peak position is not exactly at the real end of the particles' path but just before. It is an experimentally consolidated practice to assume that the particle range measurement corresponds to the distance

**Figure 7.** *Measured values of the range vs. the corresponding proton energy at TIFPA and resulting data fit.*

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

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)):

$$\mathcal{R} = \mathcal{a} + \mathcal{b} \cdot E^{1.75} \tag{1}$$

where *R* is the range of the protons in the RRD, *E* is the kinetic energy at the entrance of the RRD, and *a* and *b* are free parameters of fit.

The same measurement was performed at TIFPA with proton energy in the range between 70 and 250 MeV and with a high-intensity beam, up to 109 protons per second.

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 TIFPA, is shown.

### **5. Beam profile measurement**

The PSD can work as a profilometer at rate up to 109 particles per second therapy conditions. It is able to measure the size and the position of the beam spot. As a

### **Figure 8.**

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

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**Figure 9.**

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

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

consequence of the application of the channel reduction system, the beam profile can be reconstructed only if the beam spot size is lower or equal to the width of a ribbon (about 2 cm). The PSD was tested as a profilometer at TIFPA, where the beam optics causes a reduction of the beam spot size with increasing energy. In the

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 detec-

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

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

particles per second on average).

test, the PSD worked properly at high energies, as shown in **Figure 8**.

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

**6. The proton radiography**

tors were simultaneously active.

at low beam intensity (imaging conditions, about 106

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

consequence of the application of the channel reduction system, the beam profile can be reconstructed only if the beam spot size is lower or equal to the width of a ribbon (about 2 cm). The PSD was tested as a profilometer at TIFPA, where the beam optics causes a reduction of the beam spot size with increasing energy. In the test, the PSD worked properly at high energies, as shown in **Figure 8**.
