Development of an array-type prompt gamma detection system for the online measurement of the range of the proton beam in a patient: a Monte Carlo feasibility study

Abstract

Recently a prototype prompt gamma scanner system, named the PGS (prompt gamma scanner), was constructed and used to demonstrate that there is a clear correlation between prompt gamma distribution and the range of the proton beam in a patient. However, the PGS system requires a scanning process to obtain the prompt gamma distribution; consequently, it cannot be used in "spot scanning", in which the proton beam is continuously moving during treatment. The present Monte Carlo study explored the feasibility of a new detection system that does not require a scanning process, that is, that uses a linear array of scintillation detectors and photodiodes for online measurement of the proton beam range. The simulation results are very encouraging, showing that an array-type prompt gamma detection system can measure the proton beam range despite the fact that, with this system, the level of background gammas somewhat increases as a result of reduced collimator shielding. This paper discusses those simulation results, as well as some important design considerations based on them.