TRACK STRUCTURE APPROACHES TO THE INTERPRETATION OF RADIATION EFFECTS ON DNA

Four different, but related, model approaches are presented to evaluate DNA damage, based on radiation track structure simulations. The first model considers frequencies of clusters of energy deposition in microscopic volumes and seeks those that correlate with biological effectiveness; these appear to be of 2-10 nm dimension. The second model uses a track segment type analysis of the radiation in order to produce an energy deposition model at the nanometre level. Using this model, events occurring in structured model targets, representing DNA, are considered to be related to breaks in the DNA. The third model uses Monte Carlo track structure calculations for structured cells and discriminates between direct and indirect contributions to single and double strand breaks. The fourth model also uses Monte Carlo methods to simulate the chemical evolution of water radicals surrounding DNA to calculate the ratios of direct to indirect effects for different parameters.