Speaker
Description
Ion beam therapy effectively treats radiation-resistant and deeply located tumors but requires meticulous planning due to wide safety margins imposed by current technology. Proton transmission imaging, using protons instead of x-rays for image acquisition, is pivotal for precise treatment planning by directly probing the proton stopping power, reducing uncertainties, and enabling real-time monitoring. In the last 15 years, proton imaging prototypes have primarily used calorimeter detectors. An alternative method measures proton Time Of Flight (TOF) to determine velocity and, subsequently, residual kinetic energy. The performance and potential of TOF-based proton tomography have been recently evaluated by 1.
The TOFpRad project aims to create a proton radiography prototype integrating a Time Of Flight (TOF) system and plastic scintillating fibers to monitor the position, direction, and residual energy of therapeutic protons. A preliminary experimental apparatus was developed and tested at the National Center for Oncological Hadrontherapy (CNAO, Pavia), consisting of the following components (see the left panels of the figure for the scheme and the picture of the experimental set-up):
- layers of scintillating fibers at the beam exit, serving as a beam monitor and used to identify the position of the particles with a granularity of about 1 mm;
- a water-equivalent phantom with the possibility of creating an air gap;
- a plastic scintillator start counter at the phantom exit. It consists of two homogeneous layers of plastic scintillator (EJ-232 from Scionix), each with a thickness of 500 $\mu$m, read-out by SiPMs (Advansid NUV3S);
- the TOF-Wall detector of the FOOT experiment 2, serving as the stop detector, which was placed at approximately 215 cm from the start counter. The detector is composed of two orthogonal layers of plastic scintillating bars read-out on both sides by SiPMs. The adoption of two scintillating layers allows the identification of the interaction position of the proton in the detector, used for the correction of the timing information according to the hit position along the bar. The TOF-Wall detector is composed of 20 + 20 plastic scintillating bars (EJ200 by Eljen Technology) with a dimension of 0.3 x 2 x 44 $cm^3$ wrapped with Enhanced Specular Reflector film (ESR) to maximize the light output.
TOF measurements were performed using proton beams with energy ranging from 62 to 228 MeV. A comparison between the acquired data and the simulated data was conducted. This comparison illustrated a linear correlation between the system's response and the Monte Carlo simulation output for the energies under examination.
Additionally, other measurements were carried out by varying the size of the air gap (2-10 mm) and its position along the phantom axis. A picture of the phantom with a 5 mm air gap positioned at the center, occupying half of the phantom's volume, is shown in the figure at the top right. A preliminary analysis of the acquired data demonstrated that the developed system is able to discriminate air gaps of a few millimeters in the water-equivalent phantom, the TOF profile obtained for an air gap of 5 mm is depicted in the figure at the bottom right as an example. Moreover, a TOF dynamic response with the thickness of the air gap in the investigated range was observed, provided that a calibration of the system has been performed. This contribution will present an overview of the project and the outcome of a more thorough data analysis, as well as future perspectives for the data takings.
References:
1 N. Krah et al.: Relative stopping power precision in time-of-flight proton CT //doi.org/10.48550/arxiv.2112.11575
2 M. Morrocchi et al.: Performance evaluation of the TOF-Wall detector of the FOOT experiment //doi.org/10.1109/TNS.2020.3041433
