Ionization clustering on charged particle tracks as a seed for biologically relevant radiation effects

We construct a statistical framework for investigating the physical origins of radiation effects on biological materials and report the fit of an analytical statistical model to rates of simple lesions in DNA. Modeling primary ionization damage as trails of electron vacancies left on the trajectories of fast charged particles, we derive the dependence of rates of spatial clustering on ionization density [linear energy transfer (LET)]; a clustering scale parameter, r_{0}; and number per cluster. Published experimental results on rates of single strand breaks and base lesions in dry DNA over a range of LET are fitted with the derived functions, assuming clusters of 1 or ≥1. The fits yield reasonable goodness of fit and values of r_{0} that are consistent with expectations. Limitations of the model and future developments are discussed. This framework may ultimately contribute to an improved understanding of the physical origins of biological radiation effects.