Proton Radiography to Improve Proton Radiotherapy: Simulation Study at Different Proton Beam Energies

To improve the quality of cancer treatment with protons, a translation of X-ray Computed Tomography (CT) images into a map of the proton stopping powers needs to be more accurate. Proton stopping powers determined from CT images have systematic uncertainties in the calculated proton range in a patient of typically 3–4% and even up to 10% in a region containing bone. As a consequence, part of a tumor may receive no dose, or a very high dose can be delivered in healthy tissues and organs at risks (e.g. brain stem). A transmission radiograph of high-energy protons measuring proton stopping powers directly will allow to reduce these uncertainties, and thus improve the quality of treatment. The best way to obtain a sufficiently accurate radiograph is by tracking individual protons traversing the phantom (patient). In our simulations, we have used an ideal position sensitive detectors measuring a single proton before and after a phantom, while the residual energy of a proton was detected by a BaF2 crystal. To obtain transmission radiographs, different phantom materials have been irradiated with a 3 × 3 cm2 scattered proton beam, with various beam energies. The simulations were done using the Geant4 simulation package. In this study, we focus on the simulations of the energy loss radiographs for various proton beam energies that are clinically available in proton radiotherapy.