A Monte-Carlo-based Study of a Single-2D-detector Proton-Radiography System.

PURPOSE:To assess the feasibility of a proton radiography (pRG) system based on a single thin pixelated detector for water-equivalent path length (WEPL) and relative stopping power (RSP) measurements.METHODS:A model of a pRG system consisting of a single pixelated detector measuring energy deposition and proton fluence was investigated in a Geant4-based Monte Carlo study. At the position directly after an object traversed by a broad proton beam, spatial 2D distributions are calculated of the energy deposition in, and the number of protons entering the detector. Their ratio relates to the 2D distribution of the average stopping power of protons in the detector. The system response is calibrated against the residual range in water of the protons to provide the 2D distribution of the WEPL of the object. The WEPL distribution is converted into the distribution of the RSP of the object. Simulations have been done, where the system has been tested on 13 samples of homogeneous materials of which the RSPs have been calculated and compared with RSPs determined from simulations of residual-range-in-water, which we refer to as reference RSPs.RESULTS:For both human-tissue- and non-human-tissue-equivalent materials, the RSPs derived with the detector agree with the reference values within 1%.CONCLUSION:The study shows that a pRG system based on one thin pixelated detection screen has the potential to provide RSP predictions with an accuracy of 1%.