Technical Note: An hybrid parallel implementation for EGSnrc Monte Carlo user codes

PURPOSE: The purpose of this study was to present a parallel solution for the EGSnrc Monte Carlo code system combining MPI and OpenMP programming models as an alternative to the provided implementation, based on the use of a batch-queueing system (BQS). METHODS: Relying on a previous implementation based on OpenMP by E. Doerner and P. Caprile [Med. Phys. 44, 6672 (2017)], this work incorporates MPI features to efficiently distribute the simulation on current high-performance computing (HPC) systems. These features are introduced through properly defined macros, which are enabled depending on the compilation flags given by the user. The presented solution was benchmarked using the DOSXYZnrc code for a 6 MV clinical photon beam impinging on an homogeneous water phantom. RESULTS: The platform validation against the serial run results confirmed that the introduction of new features does not modify the final dose distribution. The performance tests indicated that the new implementation was able to handle efficiently the workload distribution among the computing units available. Using all the resources available, the hybrid simulation was 10% faster than the MPI only solution and 30% faster than the BQS implementation. CONCLUSIONS: The hybrid method presented is a viable solution to parallelize MC simulations using the EGSnrc codes in distributed computing systems in an simple and efficient way, taking advantage of the available resources and giving the user the possibility of choosing between different parallelization schemes (only OpenMP/MPI or a combination of both).