Monte Carlo simulation in PET instrumentation

Abstract

Proton therapy is one of the most precise modalities of external radiation therapy. Compared to the conventional photon therapy, due to the present of Bragg Peak, proton therapy has a much lower entrance dose and no dose beyond the target volume. Meanwhile, due to this special feature, there is a high accuracy requirement of the treatment delivery. There are different methods for verifying the spatial distribution and the range of the delivered dose. One of these measurement methods is using Position Emission Tomography (PET), which requires a simulation of the expected positron emitter distribution and compare it with the PET measurements during (i.e. in-beam) or after (i.e. in-room) the treatment. In this study, based on GATE (Version 6.2), running on vGATE (Version 2.1), a four-detector “in-beam” PET scanning system is evaluated using Monte Carlo Simulation methods. In addition, Oxygen-15, which is one of the positron emitting isotopes generated from proton irradiation, is also simulated. The installation of GATE is validated by comparing the simulation results to the benchmarking results provided by the code developers. After that, the technical performance characteristics of the four-detector “in-beam” PET scanning system, such as scatter fraction, random fraction, sensitivity and spatial accuracy have been evaluated and compared to another eight-detector “in-room” PET scanning system. The simulations demonstrate some determining factors, such as the diameters of the cylindrical phantom, the locations and activities of the sources, and etc., which can affect the technical performance characteristics of both the scanning systems.