An optimal design of beam shaping assembly for BNCT based on 7Li(p,n)7Be of 3.5 MeV proton accelerator

Accelerator-based neutron sources offer an attractive alternative to nuclear reactors for boron neutron capture therapy (BNCT) due to their unique advantages, including low cost, safety, and the feasibility of hospital installation. In this study, a series of simulations were performed based on a 3.5 MeV proton beam with a current of approximately 10 mA. This paper proposes an optimized beam shaping assembly (BSA) based on the Li37(p,n)Be47 {}_3^7{\rm{Li}}({\rm{p}},{\rm{n}}){}_4^7{\rm{Be}} neutron production reaction. The optimal target thickness was determined by considering both the neutron yield and the proton Bragg peak. The basic standards of the International Atomic Energy Agency (IAEA) were adopted as guidelines for the BSA design, and various neutron moderating materials as well as different gamma filter materials were evaluated. The performance of the designed neutron beam was further evaluated using a modified Snyder head phantom, taking into account the relevant parameters and dose profiles in irradiated tissues. In the simulations, boron concentrations of 30 ppm in tumor tissue and 10 ppm in healthy tissue were set. The results show that the same conclusion is reached regardless of whether the maximum tolerable dose to the skin (11 RBE-Gy) or that to normal tissue (12.5 RBE-Gy) is considered. A maximum dose can be delivered to the tumor site within 40 minutes of neutron irradiation, and the advantage depth is determined to be 9.2 cm.