Nanometer site analysis of electron tracks and dose localization in bio-cells exposed to X-ray irradiation

This paper reports on a Monte Carlo simulation analysis of the ionization and excitation clusters in electron tracks, which may contribute to radiation damage of biological cells with high probabilities. The study is aimed at investigating the energy transfer to the cell nucleus exposed to X-rays from low doses in the environment to high doses in radiation therapy. As an example, we adopt a water phantom exposed to X-rays from a 6 MV linac to calculate the expected energy transfer to electrons in liquid water. A track simulation of the electrons produced by the photon interactions was performed. The behavior of low energy electrons below 1 keV is of particular importance in forming clusters of ionization and excitation events within a nanometer scale (<100 nm). We describe the clustering pattern in terms of aggregation index, the distribution of point-to-point distance below several nanometers between the events. By comparing the distribution with that of the Poisson configuration, the clustering effects of the events including successive radical processes are evaluated.