Development of Linear Interpolation System for SMK Model Parameters Evaluated from Cellular-Scale Simulation (LISMEC) and its application to BNCT dosimetry.

Boron neutron capture therapy (BNCT) utilizes high linear energy transfer (LET) α-particles and 7Li ions generated through the 10B(n, α)7Li reaction. Precise dosimetry is essential for maximizing therapeutic efficacy while minimizing normal tissue adverse events, considering the microscopic distribution of 10B and cellular structures. Recently, the photon isoeffective dose (DisoE) has been proposed as a more appropriate metric for BNCT treatment planning and can be evaluated using the stochastic microdosimetric kinetic (SMK) model. However, clinical implementation of the SMK model remains challenging due to the difficulty of evaluating its input parameters, which requires computationally intensive radiation transport simulations at the cellular scale. To address this issue, we developed LISMEC (Linear Interpolation System for Stochastic Microdosimetric Kinetic model parameters Evaluated from Cellular-scale simulation), a rapid estimation framework based on precomputed cellular-scale PHITS (Particle and Heavy Ion Transport code System) simulations covering various cell geometries and boron distributions. By applying a linear interpolation algorithm, LISMEC enables the retrieval of SMK model parameters without the need for computationally intensive cellular-scale simulations. The utility of LISMEC, in conjunction with PHITS, was demonstrated through simulations of various irradiation scenarios in reactor-based BNCT. The results showed that DisoE values ranged from 7.4 to 32.7 Gy, even under a fixed macroscopic 10B concentration of 60 ppm. These findings emphasize the importance of incorporating a microscopic distribution of 10B and cellular structures into BNCT treatment planning.