MODELING 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 e ffectiveness of different energy photon radiations and tritium beta-pa rticles. Materials and methods: Modelling is carried out by Monte Carl o and includes consideration of direct energy depositions in DNA molec ules, the production of species, their diffusion and interactions with each other and DNA. Computer-generated electron tracks in liquid wate r are used to model energy deposition and to derive the initial positi ons 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-1MeV and tritium beta-particles are considered. Results: A tentative increase for dsb yield has been predicted for 70keV photon s and tritium compared with Cs-137. This increase is more pronounced f or complex dsb. Double-strand breaks are much more prone compared with ssb to combine with additional strand breaks and base damage, which c ontributes to break complexity. At least half of DNA breaks are hydrox yl radical mediated. Conclusions: The developed model makes prediction s compatible with features of available experimental data. Break compl exity has to be addressed in biophysical modelling when the relative e ffectiveness of radiations in DNA damage is studied. Obtained data str ongly argue against the dominance of direct radiation action in DNA da mage in the cellular environment predicted by some theoretical studies .