Monte Carlo Simulation of Performance of a Time-Resolved Range Telescope Using Selected Image Quality Assurance Phantoms

The superior dose conformation from protons is attributed to the Bragg peak near the end of the proton range. One challenge in proton cancer treatment is to assess the proton range fluctuations due to organ motion such as respiration. A time-resolved proton range telescope that measures coordinates, direction cosines, and the residual range of each proton can be useful in detecting and quantifying variations in radiological path length during the course of proton radiotherapy. In this paper, the Monte Carlo N-Particle eXtended (MCNPX) code was used to simulate the range telescope and study the image quality. To validate the MCNPX simulations, a simulated proton radiograph was compared with an experimentally acquired film for the same phantom. In addition, four quality assurance phantoms were simulated to investigate the quality of simulated proton radiography. Finally, the methods were applied to one phase of a patient four-dimensional computed tomography (4DCT) data set for proton radiography simulations. The results indicate that Monte Carlo simulations offer data that are useful in analyzing image spatial and temporal resolutions. Simulations show that it is useful to quantify the tumor position changes due to respiration by using a proton telescope.