Monte Carlo simulation of DNA damage by low LET radiation using inhomogeneous higher order DNA targets.

To test possible effects of the heterogeneous nature of the cell nucleus on simulation results of radiation-induced DNA damage, inhomogeneous targets have been implemented in the biophysical code PARTRAC. The geometry of the DNA and the histones was defined by spheres around the constituent atoms. Electron cross sections in liquid water were scaled according to the mass density of the different materials, whereas photon cross sections were derived from the sum of the cross sections for the constituent atoms. In the case of higher energy electrons the simulations show an increase of energy deposition in the DNA proportional to its high mass density. For photons with energies in the range of the carbon and the oxygen K-shell (0.28-0.53 keV), cross sections of DNA are larger than those of water, leading to an increased yield of strand breaks per average absorbed dose in the cell nucleus.