Radionuclides and committed internal exposure dose for radioactivation in boron neutron capture therapy

Although boron neutron capture therapy (BNCT) causes minimal damage to normal cells, accurately estimating the exposure dose based on radiation protection is crucial. This study was aimed at estimating the amount of radionuclides required for radioactivation and the internal exposure dose in BNCT by simulation calculations considering factors that were not taken into account in previous studies. This study was performed with reference to the BNCT clinical studies conducted at a reactor-based BNCT facility. Five irradiated parts of the head and neck regions were selected for estimation. The contribution of each radionuclide to the equivalent dose in each organ indicated that the effects of ²⁴Na, ³²P, and ¹²⁸I were significant. ²⁴Na is uniformly distributed throughout the body. The contribution of ³²P to the bone surface and red marrow was remarkable. Because ¹²⁸I is produced only in the thyroid, its effect was small, depending on the irradiated part. The calculated effective dose was one order of magnitude lower than that of the external exposure. Therefore, internal exposure is not negligible for exposure dose estimation in BNCT, and it is necessary to consider the irradiation component in treatment planning to avoid exposure to certain critical organs.