THE ONE CINETIC MODEL DAMAGE OF CELL BY SMALL DOSES OF RADIATION

To explain the known differences in the dose and age dependences of radiogenic mortality from leukemia and solid tumors after single exposure, a model was developed, which is a modification of the Kellerer-Rossi theory of dual radiation action. The model assumes formation in a cell of both single and double primary damages due to radiation and other carcinogens, while the recovery rate of single damages (φ) significantly exceeds that for double ones (ψ). Upon achieving a certain stage of the cell cycle (the critical age of cell – T), double damages become permanent and with probability of А can be inherited to daughter cells as “premalignant” defects. In contrast, in the Kellerer-Rossi theory, permanent damage is formed immediately after formation of the second damage at the next energy absorption event in the cell, i.e. ψ=0 .On the assumption that the premalignant defects only occur based on the double primary damages, i.e. φ>>ψ, the expressions for А were derived for the prompt radiation exposure and radiation exposure at a constant dose rate. They reproduce the effect increasing with decreasing of T, whereas the influence of T on the linear term of the dose expression in both cases is the same, but with decreasing of T the quadratic term increases faster for exposure at a constant dose rate than that for the prompt one. Thus, presence of the quadratic term in the dose expression for leukemia and its virtual complete absence for solid tumors may be due to lower T-value for hemopoietic stem cells. Predicted by the model dose rate influence on the quadratic term does not depend on the dose, so the reduction factor should be only applied to the quadratic term of the dose expression. This follows as well from the original version of the Kellerer-Rossi theory.