Optimized GPU-accelerated Monte Carlo program for real-time dose estimation directly using mesh-type computational phantoms

Mesh-type phantoms represent the latest generation of human computational phantoms, offering high resolution and adjustability advantages for individualized radiation dosimetry. Current dosimetry computation methods, which require conversion to tetrahedral mesh models for efficient Monte Carlo simulations, still do not meet the requirements for real-time dose calculations. Advancements in heterogeneous computing now allow for significant acceleration in mesh-type phantom calculations by utilizing both high-performance hardware and efficient algorithms. This study aims to develop a GPU-accelerated Monte Carlo simulation method that directly utilizes mesh-type phantoms to further enhance the speed of human dose calculations without the need for tetrahedralization. For the boundary representation polygonal models, this study redesigned and implemented the entire procedural flow of the GPU-accelerated Monte Carlo program, developing particle transport methods within the mesh-type model. All triangular facets of the mesh-type model were constructed into a tree-like acceleration structure and the traversal access pattern was optimized. Moreover, this study adopted an event-based transport method, transporting particles step-by-step by particle type, and a bias-based variance reduction technique employing geometric weights was integrated. For typical external irradiation scenarios, dose calculations between Geant4 and our GPU-based program were compared to assess computational accuracy and efficiency. Compared to the benchmark simulations conducted on a single-thread CPU via Geant4, the organ dose discrepancies calculated by the GPU-accelerated program generally remained within a 5% margin, while computational times were reduced by factors ranging from 500 to 50000. To our knowledge, this study is the first to utilize a mesh-type model for GPU-accelerated dose calculation without tetrahedralization. The simulation time has been dramatically reduced from hours to just mere seconds, offering a rapid and precise Monte Carlo method for mesh-type computational phantoms. This development supports real-time dose calculation studies using dynamic mesh-type models, providing a robust Monte Carlo simulation tool.