Study of BNCT neutronics optimization for out-of-beam dosimetry based on radiobiological figures of merit

This work addresses the neutronic design of a Beam Shaping Assembly (BSA) that is appropriate for a Accelerator-based Boron Neutron Capture Therapy (AB-BNCT). Instead of designing a moderator utilizing the IAEA-1223 recommendation and in-phantom figure of merit, in this work we study neutronics to decrease the out-of-beam dosimetry by employing radiobiological figures of merit to assess the beam quality. In particular, in the radiobiological probability model, we include two normal tissue cases, and accordingly optimize the thickness and cone angle of the collimator. Hence, in this study, for a large opening diameter, i.e., 10 cm, we use a small cone angle, which can decrease the out-of-beam dosimetry effectively. Accordingly, for a small opening diameter, i.e., 2 cm in this study, we employ a large cone angle to guarantee that the neutron flux is large enough. Our simulation results demonstrate that the neutronics optimization of the collimator is a tradeoff between the out-of-beam dosimetry and the neutron flux. From our findings, we conclude that upon considering radiobiological figures of merit, collimators with a tunable design shape are more appealing due to adapting to different treatment situations.