An extended photon isoeffective dose model accounting for the energy‐dependent effectiveness of secondary charged particles in BNCT

BACKGROUND: The absorbed dose in Boron Neutron Capture Therapy (BNCT) arises from various radiation components, each contributing differently to the overall biological effect. These effects depend not only on the absorbed dose but also on the type and energy of the involved secondary charged particles. Current dosimetric models convert absorbed dose into an equivalent photon dose using radiation-specific weighting factors that account for some differences in radiation type. However, these models generally neglect the energy dependence of biological effectiveness. PURPOSE: To evaluate the relevance of incorporating the energy dependence of secondary charged particles into BNCT dosimetry, and to assess its impact on dose calculations and clinical outcome estimations. METHODS: , with varying levels of detail regarding energy and radiation fields representation, were evaluated across three scenarios. The analysis moved from a simplified geometry using a cylindrical phantom irradiated with epithermal neutrons, to progressively more realistic clinical scenarios, including a head and neck cancer treatment planning case and a retrospective study of a cutaneous melanoma case treated with BNCT at the RA-6 reactor in Argentina. RESULTS: ), thus raising the potential radiotoxicity risk. An apparent gain in TCP resulted from overestimating the required treatment time due to oversimplified modeling. In the retrospective melanoma case irradiated with the RA-6 mixed thermal-epithermal beam, simplified models underestimated the skin dose by 8% to 12%, potentially compromising dose-response interpretations. CONCLUSIONS: Beyond treatment planning, accurate dose modeling is also key for outcome assessment and meaningful comparisons with photon radiotherapy. Incorporating detailed LET-dependent RB modeling is especially important in scenarios involving low-to-moderate boron concentration levels or superficial tissues, where recoil protons dominate the dose composition. In contrast, simplified models may be acceptable in boron-rich, high-LET contexts, particularly when constrained by limited radiobiological data or computational resources. These findings support the development of a flexible photon isoeffective dose formalism that can evolve alongside advances in BNCT technologies and RB data.