Optimization of a B4C/graphite composite energy degrader and its shielding for a proton therapy facility

Proton therapy is an advanced cancer treatment modality due to its ability to precisely deliver radiation doses to tumors using the Bragg peak effect. An energy degrader plays a vital role at a cyclotron-based proton therapy facility, as it provides a rapid, reliable, and reproducible method of setting the appropriate beam energy for radiotherapy. However, the protons undergo nuclear interactions with the matter in the degrader, leading to significant secondary particles causing a large ambient radiation dose nearby, creating severe risks for the facility operation. This study investigated the beam loss mechanism and the secondary particle generation in a B4C/graphite composite (BGC) energy degrader. Monte Carlo simulations were performed to ensure the shielding design's reliability. Calculations showed that the BGC degrader had a higher beam transmission efficiency than a pure graphite degrader, while the secondary neutron yield was higher. An optimum shielding configuration can significantly reduce the radiation dose to an acceptable level for sensitive devices and maintenance staff.