Influence of D₂O substitution on BNCT dosimetry with the AB-BNCT system: A combined Monte Carlo and experimental...

Boron neutron capture therapy (BNCT) faces challenges in delivering sufficient therapeutic dose to deep-seated tumors due to limited neutron penetration. Previous studies indicate that replacing tissue light water (H₂O) with heavy water (D₂O) can enhance neutron penetration while reducing photon dose under specific conditions. However, the applicability of this method within the NeuPex accelerator-based BNCT system requires further investigation and validation. In this study, Monte Carlo simulations with a radiation computational phantom quantified D₂O substitution effects on BNCT dosimetry for the NeuPex system, complemented by experimental measurements in a water phantom to assess neutron penetration depth and photon dose reduction. Simulation results indicate that when tumor depth exceeds 6 cm, D₂O substitution enhances the dosimetric performance of BNCT within the tumor. At a tumor depth of 7 cm, 20% D₂O substitution increases the tumor minimum dose by 14.1% and D₈₀ by 8.2%. Experimental results further demonstrate that D₂O substitution enhances neutron penetration while reducing photon dose contamination. With 20% D₂O substitution, the reaction rate increases beyond depths of approximately 6 cm. This study demonstrates the feasibility and applicability of D₂O substitution in the NeuPex system, establishing a theoretical foundation for future clinical implementation strategies.