Monte Carlo evaluation of DNA fragmentation spectra induced by different radiation qualities

The PARTRAC code has been developed constantly in the last several years. It is a Monte Carlo code based on an event-byevent
description of the interactions taking place between the ionising radiation and liquid water, and in the present version
simulates the transport of photons, electrons, protons, helium and heavier ions. This is combined with an atom-by-atom representation
of the biological target, i.e. the DNA target model of a diploid human fibroblast in its interphase (genome of 6
Gigabase pairs). DNA damage is produced by the events of energy depositions, either directly, if they occur in the volume
occupied by the sugar–phosphate backbone, or indirectly, if this volume is reached by radiation-induced radicals. This requires
the determination of the probabilities of occurrence of DNA damage. Experimental data are essential for this determination.
However, after the adjustment of the relevant parameters through the comparison of the simulation data with the DNA fragmentation
induced by photon irradiation, the code has been used without further parameter adjustments, and the comparison
with the fragmentation induced by charged particle beams has validated the code. In this paper, the results obtained for the
DNA fragmentation induced by gamma rays and by charged particle beams of various LET are shown, with a particular
attention to the production of very small fragments that are not detected in experiments.