Ion-induced electron production in tissue-like media and DNA damage mechanisms

This work is the first stage in the development of an inclusive approach to calculation of the DNA damage caused by irradiation of biological tissue by ion/proton beams. The project starts with an analysis of ionization caused by the projectiles and the characteristics of secondary electrons produced in tissue-like media. We consider interactions with the medium on a microscopic level and this allows us to obtain the energy spectrum and abundance of secondary electrons as functions of the projectile's kinetic energy. The physical information obtained in this analysis is related to biological processes responsible for the DNA damage induced by the projectile. In particular, we consider double strand breaks of DNA caused by secondary electrons and free radicals, and local heating in the ion's track. The heating may enhance the biological effectiveness of electron/free radical nteractions with the DNA and may even be considered as an independent mechanism of DNA damage. Numerical estimates are performed for the case of carbon-ion beams. The obtained dose-depth curves are compared with results of the MCHIT model based on the GEANT4 toolkit.