Repopulation of 'normal tissue' from the view of the nominal standard dose (NSD) concept and of a two-compartment model

On the basis of the NSD concept the time course of repopulation of normal tissue after irradiation was studied and compared with the results of a two-compartment model of proliferation kinetics. According to Ellis' concept repopulation goes on slowly and does not lead to a complete recovery of the normal tissue. The course of repopulation essentially depends on the dose and may be varied by differentNSD values. Comparisons with the two-compartment model, which yields a likewise dose-dependent but essentially steeper course of repopulation modified by repopulation limit values, permit the conclusion that the NSD value to a tissue is determined by its primary radiosensitivity as well as by the rate of repopulation which may still be tolerated by the type of tissue as the consequence of a fractionated irradiation series. (author)