Comparison of two methods simulating inter-track interactions using the radiobiological Monte Carlo toolkit TOPAS-nBio.

Objective. To compare two independently developed methods that enable modelling inter-track interactions in TOPAS-nBio by examining the yield of radiolytic species in radiobiological Monte Carlo track structure simulations. One method uses a phase space file to assign more than one primary to one event, allowing for inter-track interaction between these primary particles. This method has previously been developed by this working group and published earlier. Using the other method, chemical reactions are simulated based on a new version of the independent reaction time approach to allow inter-track interactions. Approach. G -values were calculated and compared using both methods for different numbers of tracks able to undergo inter-track interactions. Main results. Differences in the G -values simulated with the two methods strongly depend on the molecule type, and deviations can range up to 3.9% (H 2 O 2 ), although, on average, the deviations are smaller than 1.5%. Significance. Both methods seem to be suitable for simulating inter-track interactions, as they provide comparable G -values even though both techniques were developed independently of each other.