The yield of DNA double-strand breaks produced intracellularly by ionizing radiation: a review

The mechanisms of radiation damage production are used to examine these premises: (1) the number of DNA double-strand breaks per unit dose increases with dose; (2) cell type to cell type variations in yield of DNA dsb per dose occur. Two stages of damage production are identified as possible sources of damage yield modulation; numbers of OH. free radicals reacting with target, and amount of chemical repair occurring on target radicals. These factors are discussed in the light of the structures within which cellular DNA is packaged and the known rate constants for the reactions involved. It is concluded that, in the presence of oxygen: (a) the number of DNA dsb is linearly related to dose, (b) the yields of DNA damage per dose among cell types are constant. There is a caveat to the latter: the chromatin structure may be different in radiosensitive cell lines. In the absence of such difference, variations in radiosensitivity with dose or cell type are assigned to differences in repair speed and/or accuracy. (author)