Independent reaction times method in Geant4‐DNA: Implementation and performance

Abstract

Purpose The simulation of individual particle tracks and the chemical stage following water radiolysis in biological tissue is an effective means of improving our knowledge of the physico‐chemical contribution to the biological effect of ionizing radiation. However, the step‐by‐step simulation of the reaction kinetics of radiolytic species is the most time‐consuming task in Monte Carlo track‐structure simulations, with long simulation times that are an impediment to research. In this work, we present the implementation of the independent reaction times (IRT) method in Geant4‐DNA Monte Carlo toolkit to improve the computational efficiency of calculating G‐values, defined as the number of chemical species created or lost per 100 eV of deposited energy. Methods The computational efficiency of IRT, as implemented, is compared to that from available Geant4‐DNA step‐by‐step simulations for electrons, protons and alpha particles covering a wide range of linear energy transfer (LET). The accuracy of both methods is verified using published measured data from fast electron irradiations for •OH and eaq‐ for time‐dependent G‐values. For IRT, simulations in the presence of scavengers irradiated by cobalt‐60 γ‐ray and 2 MeV protons are compared with measured data for different scavenging capacities. In addition, a qualitative assessment comparing measured LET‐dependent G‐values with Geant4‐DNA calculations in pure liquid water is presented. Results The IRT improved the computational efficiency by three orders of magnitude relative to the step‐by‐step method while differences in G‐values by 3.9% at 1 μs were found. At 7 ps, •OH and eaq‐ yields calculated with IRT differed from recent published measured data by 5% ± 4% and 2% ± 4%, respectively. At 1 μs, differences were 9% ± 5% and 6% ± 7% for •OH and eaq‐, respectively. Uncertainties are one standard deviation. Finally, G‐values at different scavenging capacities and LET‐dependent G‐values reproduced the behavior of measurements for all radiation qualities. Conclusion The comprehensive validation of the Geant4‐DNA capabilities to accurately simulate the chemistry following water radiolysis is an ongoing work. The implementation presented in this work is a necessary step to facilitate performing such a task.

Recent Developments on gMicroMC: Transport Simulations of Proton and Heavy Ions and Concurrent Transport of Radicals and DNA

“…In the case of protons and heavy ions, due to the lack of experimental data, the cross-sections and models could also be associated with large uncertainties, causing concerns about the robustness of the simulation results. To reduce these uncertainties, there have been multiple experiments and models [ 13 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 ] developed in a more elaborate fashion. Yet, more studies are needed to more thoroughly understand the relevant processes.…”

A Geant4-DNA Evaluation of Radiation-Induced DNA Damage on a Human Fibroblast

“…The chemical reaction rates between the DNA molecules and radicals were those proposed by Buxton et al [ 30 ]. In this work, the reactions were added to the Geant4-DNA chemistry constructor “G4EmDNAChemistry_option3” [ 18 , 20 ].…”

Assessment of DNA damage with an adapted independent reaction time approach implemented in Geant4‐DNA for the simulation of diffusion‐controlled reactions between radio‐induced reactive species and a chromatin fiber

“…25,26 In particular, an implementation of the original IRT method has been developed and will be released soon. 25 In this work, an implementation of an IRT variant is proposed. This method is implemented in the current chemistry module of Geant4-DNA with the idea of keeping the spatiotemporal information of the radiolytic species to calculate DNA damage.…”

“…Applications are mainly related to the validation of radiolytic yields and the evaluation of radiation‐induced DNA damage. To enhance the potential of Geant4‐DNA, developments are ongoing in different groups with the goal to provide IRT methods to Geant4‐DNA users 25,26 . In particular, an implementation of the original IRT method has been developed and will be released soon 25 .…”

“…To enhance the potential of Geant4‐DNA, developments are ongoing in different groups with the goal to provide IRT methods to Geant4‐DNA users 25,26 . In particular, an implementation of the original IRT method has been developed and will be released soon 25 . In this work, an implementation of an IRT variant is proposed.…”