Optimizing Dual-layer Neutron Moderators for Accelerator-based Boron Neutron Capture Therapy: A Geant4 Simulation Study

In this study, we used Geant4 Monte Carlo simulations to explore how different two-layer combinations of moderator materials can improve the performance of accelerator-based boron neutron capture therapy (BNCT). We tested 16 pairings of aluminum oxide (Al 2 O 3 ), titanium(III) fluoride, lithium bromide (LiBr), and lithium carbonate to see how each affected neutron and gamma radiation levels-both at the beam exit and within a simulated tumor. To evaluate their performance, we applied a weighted scoring system that considered both treatment effectiveness and patient safety. Our results showed that a dual‐layer configuration of LiBr (Configuration N) delivered the highest thermal neutron dose to the tumor, making it the most effective for treatment. On the other hand, a double layer of Al 2 O 3 (configuration P) excelled in minimizing harmful radiation outside the tumor area. Some setups, like LiBr + Al 2 O 3 (configuration G), struck a good balance between efficacy and safety. These insights can help guide the development of more efficient and safer beam-shaping assemblies for clinical BNCT applications.