Preliminary study of a compact epithermal neutron absolute flux intensity measurement system for real-time in-vivo dose monitoring in boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a radiotherapy technology that selectively kills tumor cells via the ¹⁰B(n, α)⁷Li reactions. Epithermal neutrons (0.5 eV–10 keV) are emitted and converted into thermal neutrons, which have a larger neutron capture reaction cross-section, by slowing down in the human body before reaching the tumor. Recently, the development of an epithermal neutron absolute flux intensity measurement technique has become crucial for real-time in-vivo dose monitoring in BNCT. In this study, a concept for a measurement system consisting of multiple compact scintillator with optical fibers detectors covered with neutron absorbers of various thicknesses is proposed. The designed system achieves a consistent response to epithermal neutrons with a theoretical coefficient of variation not higher than 5% for both LiCAF and EJ-254 scintillators. The theoretical feasibility of the proposed measurement system was investigated by an irradiation experiment carried out at the heavy water neutron irradiation facility at the Kyoto University Reactor. The experimental results indicated that further improvement and refinement are necessary to meet the high accuracy and precision required for real-time dose monitoring in clinical applications.