Development of an Array-type Prompt Gamma Detection System for the Online Measurement of the Proton Beam Range in a Patient: a Monte Carlo Feasibility Study

Abstract

Recently a prototype prompt gamma scanner system, named PGS (Prompt Gamma Scanner), was constructed and used to demonstrate that there is a clear correlation between the 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, and 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 the online measurement of the proton beam range. The simulation results are very encouraging, showing that the 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.