Monte Carlo Dose Computation for Boron Neutron Capture Therapy (BNCT)

Sammanfattning

This thesis presents the development and validation of temperature-dependent neutron transport for a Monte Carlo dose computation prototype for boron neutron capture therapy (BNCT). The end-goal of the dose engine is to be implemented within the treatment planning system RayStation. The work focuses on incorporating thermal motion of target nuclei and molecular structure effects for hydrogen bound in water. The work used evaluated nuclear data from the ENDF/B-VIII.0 library processed using NJOY-2016. Doppler-broadened cross sections and thermal scattering law data were generated and implemented in a GPU-accelerated Monte Carlo neutron transport framework. In addition, photon transport functionality and variance reduction techniques were implemented to improve photon dose statistics. Validation was done against the general Monte Carlo transport code PHITS. The results demonstrate that the implementation of thermal motion produces good agree-ment with PHITS for both 1 eV and 1 keV neutron beam simulations. The developed prototype reproduces the overall behavior of the dose components while maintaining substantially shorter runtimes than PHITS. The variance reduction techniques for photon transport also showed improved statistics. At the same time, several discrepancies remain unresolved. The photon dose was found to be underestimated in certain validation cases, with about 5%. Furthermore, the implementation of molecular structure effects resulted in dose overestimations. Further investigation is required to achieve better agreement with PHITS. Overall, the work demonstrates that temperature-dependent neutron transport can be incorporated into a GPU accelerated BNCT Monte Carlo dose engine along with photon support. The developed framework is an important step toward a physically accurate BNCT dose engine to be implemented within RayStation. However, this work also highlighted several areas requiring further development and validation.