Monte Carlo Design Study of a Gamma Detector System to Locate Distal Dose Falloff in Proton Therapy

Monte Carlo simulations have been performed to design a prompt gamma detector system for use as a quality assurance device in proton therapy. The system measures prompt gammas emitted in the direction normal to the incident therapeutic protons to correlate with the location of the distal dose falloff. The system consists of a drift chamber to measure the energies and directions of recoil electrons and a scintillator array to measure the positions and energies of scattered gammas in coincidence with the electrons. To ensure the use of the system in a therapeutic environment, the detection rate of Compton-scattered prompt gammas was simulated. The simulation predicts that the reconstruction uncertainty is around 1 cm for a practical configuration of the detector system. The resolution of the reconstruction was evaluated for varying dimensions and energy resolutions assumed for the detector. An actual system is being constructed based on this work.