On the probability of interaction between elementary radiation-induced chromosomal injuries.

Within the Theory of Dual Radiation Action, the heuristically useful function, gamma(chi), that two energy depositions, a distance chi apart, will result in observable damage can be written in terms of two more fundamental quantities: One, s(chi), describes the structure of the sensitive matrix of the cell. The other, g(chi), describes the probability that two elementary injuries, a distance chi apart, will combine to produce observable damage. A priori, the known enhancement exhibited by gamma(chi) at nanometer separations could be due to an enhancement of s(chi), g(chi) or both. For the endpoint of chromatid exchanges in Chinese hamster cells, gamma(chi) has been evaluated from experimental data and s(chi) from a model system. From these g(chi) has been estimated and is roughly constant below approximately 1 micron, decreasing rapidly at larger separations. Thus the enhanced short-range effect appears to be a function more of the spatial characteristics of the target rather than the probability of damage interaction.