Evaluation of the KERMA approximation method in Monte Carlo dose calculations for BNCT involving a realistic 3D patient phantom.

Monte Carlo (MC) methods are generally recognized as the gold standard for dose calculations. However, achieving high statistical confidence is computationally expensive, particularly when complex secondary particles are involved. Kinetic Energy Released in Matter (KERMA) approximation method is a variance reduction technique widely used in MC simulations. This study evaluated the accuracy and efficiency of the KERMA approximation for Boron Neutron Capture Therapy (BNCT) dose calculations using the TOol for PArticle Simulation MC code. Simulations were performed on a CT phantom of a glioblastoma patient using an accelerator-based BNCT source. It was found that neutron KERMA results agreed with Analog MC results within 2%, while providing a 157-fold computational speed-up. However, the photon KERMA approximation overestimated skin photon dose by ~12%. The results suggest that the KERMA approximation for BNCT offers clinically acceptable accuracy and efficiency, while using Analog MC method for skin photon dose evaluation can further improve overall accuracy.