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

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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 bio-cells with high probabilities. The study is aimed to investigate the energy transfer to the cell nucleus exposed to X-rays from low dose in the environment to high dose in radiation therapy. As an example, we adopted a water phantom (rectangular solid, 30×30×30 cm) exposed to a linac 6 MV X-ray to calculate the expected energy transfer to electrons in liquid water. Then, a track simulation of the electrons produced by the photon interactions was performed. In the track simulation, the behavior of low energy electrons below 1 keV is of particular importance to form clusters of ionization and excitation events within a nanometer scale (<100 nm). We describe the clustering pattern in terms of aggregation index (AI), 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.
2009-04-15