Modelling DNA damage induced by different energy photons and tritium beta-particles

Purpose: To model the production of single- and double-strand breaks (ssb and dsb) in DNA by ionizing radiations. To compare the predicted effectiveness of different energy photon radiations and tritium beta-particles. Materials and methods : Modelling is carried out by Monte Carlo and includes consideration of direct energy depositions in DNA molecules, the production of species, their diffusion and interactions with each other and DNA. Computer-generated electron tracks in liquid water are used to model energy deposition and to derive the initial positions of chemical species. Atomistic representation of the DNA in B form with a first hydration shell is used. Photon radiations in the energy range 70keV-1 MeV and tritium beta-particles are considered. Results: A tentative increase for dsb yield has been predicted for 70keV photons and tritium compared with 137Cs. This increase is more pronounced for complex dsb. Double-strand breaks are much more prone compared with ssb to combine with additional strand breaks and base damage, which contributes to break complexity. At least half of DNA breaks are hydroxyl radical mediated. Conclusions: The developed model makes predictions compatible with features of available experimental data. Break complexity has to be addressed in biophysical modelling when the relative effectiveness of radiations in DNA damage is studied. Obtained data strongly argue against the dominance of direct radiation action in DNA damage in the cellular environment predicted by some theoretical studies.