• hadrontherapy
• proton imaging
• proton radiography
• time-of-flight

Hadrontherapy is a tumour treatment modality that is increasingly being used nowadays. It consists in the irradiation of cancerous tissue with accelerated heavy particles such as protons and carbon ions. The advantage of this technique resides in the way these particles lose energy in matter: they deliver most of the dose in depth to the tumour with significantly less damage to the surrounding healthy tissue. The dose trend as a function of tissue depth is called the Bragg curve and is characterised by the typical peak.
Proton radiography (pRad) and proton computed tomography (pCT) are being investigated for both diagnostic and quality control purposes since a proton imaging device would allow to obtain the patient's anatomical information directly in terms of proton Relative Stopping Power, thus eliminating the errors derived in the conversion from CT's Hounsfield Units. In recent years, with the advent of fast detectors, possible pRad and pCT devices based on particle time-of-flight calculations are being investigated. The purpose of these studies is to develop cost-effective systems ensuring an excellent time resolution and a high rate capability, as well as to overcome the limitations of calorimeters.
The purpose of this thesis is to study a prototype for time-of-flight-based proton imaging, in the framework of the Time-of-Flight proton Radiography (ToFpRad) project. The final goal is to build a system that is easy to use, space-saving and therefore compatible with proton therapy treatment rooms, and to test its imaging capability. The proposed device is composed of a scintillating fibre tracker and a time-of-flight detection system consisting of two detectors placed 2 m apart. A series of acquisitions were made at CNAO in February 2024 in order to evaluate the apparatus's applicability in hadrontherapy, testing its contrast and resolution. The prototype was calibrated and its time-of-flight performance was assessed in the energy range (62.73-228.57) MeV. Furthermore, its performance was tested acquiring data with an air-water equivalent phantom with variable air gap size and position in the phantom. Monte Carlo (MC) simulations provided a reference for the experimental data.
Overall, the device has proven to be capable of measuring time-of-flight in the therapeutic proton energy range, in fact the experimental results are in agreement with MC simulations. For this first prototype, though, the current time resolution does not meet the project final goal and tends to degrade as the proton initial energy increases. The measured time-of-flight varies linearly with the gap thickness, indicating a dynamic response to the differences in the phantom composition (air vs. water), and remains fairly constant as a function of gap depth in the phantom. Likewise, the spatial resolution can be considered approximately constant within 0.6 cm and 0.5 cm as a function of the gap width and its depth in the phantom, respectively.
This first apparatus of the project needs further modifications and investigations in order to be suitable for clinical translation. More specifically, the spatial resolution is lower than the standard CT both because the DAQ used has an acquisition data rate of 1 kHz and because the detector arrangement is not optimised. Improvements will include adjustments to the various components in order to sustain a much higher data rate and optimise the time and spatial resolution for proton detection.