Monte Carlo Study on the Performance of 200 MeV Proton Therapy Energy Degraders Made of Different Materials

Energy selection system (ESS) is an important component for medical proton cyclotron system. It has been widely used to modulate the proton energy in accordance with treatment requirements. ESS consists of the energy degrader which was mostly made of graphite. Recent years, to improve the transmission efficiency of the proton beams, beryllium and boron carbide have been proposed to substitute the graphite. In this work, the Monte Carlo code, TOPAS, was used to simulate the transport process of 200 MeV proton beams traversing the multi-wedge energy degrader made of graphite, beryllium and boron carbide, respectively. Energy fluxes of the protons and secondary neutrons after degrader, as well as the energy dispersion of the degraded proton beams, were calculated. It is found that the energy dissipation effect is nearly identical for all three kinds of degrader material, but using the beryllium or even boron carbide can improve the proton transmission efficiency. However, more secondary neutrons would be produced when proton beams interact with the beryllium and boron carbide, suggesting the need of additional consideration for radiation shielding to devices.