Purpose: Radiation transport simulations, in particular the detailed particle-by-particle modelling of Monte Carlo, provide significant insight into radiation processing scenarios. But simulations still face validation and verification challenges, akin to those encountered experimentally. There is an evident need to validate simulations, and this study takes a step towards establishing a framework to standardize simulation in radiation processing.

Methods: Independent researchers carried out a comparison using two different Monte Carlo simulation systems — EGSnrc and Geant4, the latter using Dose Insight’s virtual dose mapping tool. A systematic comparison evaluated a) geometry specifications, b) input data, c) scoring grids, and d) dose determination (absolute and relative). Additionally, the Fano test, an inherent validation technique for ionizing radiation simulation, was used.

Results: Even for simple scenarios, significant differences in the results can arise with different software if the simulation geometry, materials and physics parameters are not carefully aligned. The inputs are specified differently for the two software, so expertise with both proved useful. It was also shown that the Fano test stands as a very stringent test of simulation validity. By carefully following the outlined comparison process, the agreement shown in Figure 1 between EGSnrc and Geant4 was achieved.

Conclusions: The findings of this investigation can assist in developing a framework for a consensus-based approach to validate Monte Carlo modelling of ionizing radiation transport and standardize radiation processing simulations, leading to an approved, ongoing comparison program that runs in parallel with current experimental dosimetry programs.