Fast Monte Carlo Sampling of DNA damage for radiotherapy

Nanodosimetric simulation of DNA damage is important for understanding the differences between the biological effects of different particles. There are many emerging radiotherapy modalities which make use of the higher biological effect of high linear energy transfer particles. Simulation provides a useful tool to compare treatment modalities, but full nanodosimetric simulation of DNA damage is time and resource intensive. A fast Monte Carlo sampling method is presented to allow the dose, number of strand breaks and number of double strand breaks to be quickly sampled to allow rapid comparison of treatments. Results showed good agreement for mono-energetic simulations of α-particles and electrons in the range 0.15–7 MeV and 0.8 keV–7 MeV respectively. Except in the tail of the distribution, the reconstructed probability density function agrees within 10% of full Geant4 simulated results. The sampling method was also applied to sample the dose and DNA damage yields for the realistic scenario of diffusing alpha-emitters radiation therapy where the DNA damage is due to the products of the decay chain of 224Ra, which has a multi stage decay chain including both α- and β decays. The mean difference between the two methods for this scenario was in agreement within one standard deviation. The simulation time for this simulation was significantly reduced from approximately 20 weeks of CPU hours to less than 0.25 CPU hours.