A microdosimetric-kinetic model of cell death from exposure to ionizing radiation of any LET, with experimental and clinical applications

A model of mammalian cell death and survival following exposure to ionizing radiation that combines a kinetic description of repair and injury processes with a microdosimetric description of radiation energy deposition is presented. With reduction of one of the defining kinetic equations from quadratic to linear form, relations are obtained that describe the results of commonly performed variations of the cell survival experiment. These include single-dose survival of linear-quadratic form, survival after split-dose treatment and after post-irradiation change ill culture conditions and survival after exposure to continuously administered irradiation at low constant dose-rate. The effect of the inhomogeneous deposition of radiation energy inherent in exposure to radiation of significantly non-zero LET is included in these relations which apply to radiation of any LET. The values of the kinetic rate and time constants for repair and the processes that lead to cell death postulated in the model, which compose the alpha and beta parameters of the linear-quadratic survival relation, are estimated from cell survival experiments and DNA double-strand break measurements from the literature. A relation for estimating the daily fractional dose equivalent to continuous irradiation as employed in low dose-rate brachytherapy cancer treatment is presented.