Simulation study on a prompt gamma detection system for use in proton therapy

In proton beam therapy, it is important to know the location of the distal dose falloff. The method we adopt is to detect prompt gammas emitted from nuclear reactions in the direction normal to incident protons. While we have successfully measured the falloff locations in the therapy energy range of 100 - 200 MeV by using a scanning system, a stationary system is needed for practical applications. The new system we are developing consists of a micro-time projection chamber (TPC), which can track the Compton-scattered electrons, and a position-sensitive scintillation detector. The performance of such a system has been studied and optimized using the Monte Carlo simulation toolkits GEANT and GLECS. With coincidence information between the TPC and the scintillation camera, the prompt gammas can be reconstructed with high angular resolution to filter the normal direction. We present the simulation results for the planned system.