Study on Microdosimetry for Boron Neutron Capture Therapy

A brain tumor, a malignant melanoma and recently a head-neck cancer have been treated by Boron Neutron Capture Therapy (BNCT). Neutrons from a research reactor have been used for BNCT. The therapeutic gain of BNCT depends on intercellular distributions of B and behavior of particles generated in the tumor cell. Two typical boron compounds of BSH (sodium borocaptate) and BPA (p-boronophenylalanine) have been used for BNCT. The BSH is especially accumulated around the cell membrane and the BPA around the cell nucleus. We have studied microdosimetry concerning on behavior of α and Li particles by simulating a single and a multi-cell models, where the B distributions of BSH and BPA were assumed above accumulation conditions. The PHITS code developed in Japan Atomic Energy Agency was used for calculation of α and Li particles with nuclear data library of ENDF/B-VI. The SPAR code including in the PHITS was also used for calculation of stopping power of these particles. We also evaluated LET values of α and Li particles and dose distributions for BPA and BSH compounds by considering the influence from neighbor cells in a multi-cell model.