Simulation of strand break induction by DNA incorporated 125I

Monte Carlo calculation of 125I Auger cascades has provided electron spectra for individual decays with kinetic energies determined by Dirac-Fock methods. For these Auger electrons, track structures in liquid water have been generated and superimposed on a straight DNA plasmid model with atomic coordinates taken from X ray diffraction studies. Due to its high geometrical resolution, this DNA model makes it possible to localize the energy deposition or/and radical production events relative to the submolecular units of the DNA strands (base, sugar, phosphate). Furthermore, it is possible to distinguish between events inside (direct) and outside (indirect, radical production) of the atomic volumes of the DNA. On the basis of different assumptions for the effectiveness of strand break induction by direct hits and by OH· and H· radicals, the yields for single- and double strand breaks, as well as the strand break distribution as a function of the distance from the decay site, has been evaluated and compared with experimental and theoretical results from the literature