Mathematical model of normal tissue involvement in gamma teletherapy

: A model of normal tissue injury as a result of exposure to ionizing radiation is based on an assumption that the degree of tissue injury is determined by the degree of destruction by certain critical cells. The dependence of the number of lethal injuries on a single dose is expressed by a trinomial - linear and quadratic parts and a constant, obtained as a result of the processing of experimental data. Quantitative correlations have been obtained for the skin and brain. They have been tested using clinical and experimental material. The results of the testing point out to the absence of time dependence on a single up to 6-week irradiation courses. Correlation with an irradiation field has been obtained for the skin. A conclusion has been made as to, first, time lag blurring time dependence within a certain range of courses, second, the presence of a component of true regeneration of which the degree depends on the volume irradiated. Proceeding from such an understanding of injury-regeneration processes a conclusion has been made that the concept of isoefficacy of irradiation courses is conditional. Volume-time fractionation is a promising direction in the development of radiation therapy.