Cancer can be treated by irradiation with protons (proton therapy). The radiation dose deposited by protons in the patient is low at the entrance, high at the end of their range (distance where they stop), and zero after. The initial proton energy is tuned such that protons stop and deposit most of the dose in the tumor while sparing healthy tissues. However, range uncertainties affecting treatment plans prevent from fully exploiting this potential dose benefit. Uncertainties arise from converting X-ray-CT images of the patient into relative stopping power (RSP) maps, describing the local energy loss of protons in tissues, determining the predicted range. These uncertainties can be reduced by imaging the patient with protons and using the proton image information to improve the X-ray-CT-based RSPs. The most immediate way is measuring the integral RSP along the proton path in one direction (proton radiography (pRG)) with a compact detector.
In this thesis of Francesco Olivari, we investigated the feasibility of pRG with one thin 2D-pixelated detector measuring the integral energy deposited and the number of protons to determine the RSP. The system was first simulated, showing its potential of measuring 1% accurate RSPs. Then, its feasibility with a scintillator screen coupled with a CCD camera, and with a Timepix semiconductor chip was investigated. With the Timepix, another method was also considered tracking the individual protons and measuring the most frequent individual energy deposit. The results are analysed and future experiments for their improvement are proposed. Finally, the clinical implementation of the system is discussed.
