The Neutron Energy Spectrum Obtained Using Energy Spectrum Superposition Method for Boron Neutron Capture Therapy

Abstract

The neutron energy spectrum and fluence rate constitute critical determinants of tumor absorbed dose and therapeutic efficacy in neutron capture therapy (NCT). Variations in tumor depth and morphology, combined with accelerator beam intensity fluctuations, make it challenging to quickly obtain an accurate neutron energy spectrum. This study develops an energy spectrum superposition method (ESSM) that enables rapid neutron spectrum reconstruction through parameter retrieval from precomputed neutron transport databases. The methodology is validated using a beam shape assembly (BSA) with the three-layer moderator of aluminum fluoride (AlF3)-32.5 cm, CaF2-22.5 cm, and titanium fluoride (TiF3)-2 cm. Compared to the traditional simulation-based method, the energy spectrum obtained by ESSM demonstrates improved smoothness and superior statistical quality. For the two physical processes—proton bombardment on the target and neutron injection into the BSA—the neutron fluence rate ratios relative to the ESSM and the traditional simulation-based method were 0.958 and 0.996, respectively. After integrating the two physical processes, the BSA’s emission window demonstrated a fluence rate ratio of 0.977. Furthermore, when the number of calculated particles is $3\times 10^{{8}}$ , the equivalent computation efficiency is a 16500-fold enhancement, which can significantly reduce the time needed to calculate. The achieved rapid calculation demonstrates clinical viability for real-time treatment planning system (TPS) operation during image-guided boron NCT (BNCT) procedures.