[Dose-time optimization in fractionated radiotherapy]

On the basis of an evaluation of different isoeffect correlations for normal tissue reactions supported by a clinical study, a number of correlations for the dose-time optimization of irradiations with equal fractionation intervals are derived from a simple approach for the survival rate of irradiated tumor cells based on a linear quadratic dose-effect function for an exponential cell proliferation. This allows to determine optimum single doses for every given fractionation interval which, applied with the number of fractions tolerated by normal tissue, lead to a maximum reduction of tumor cells. The values of these optimum fractionation parameters depend from cell proliferation and radiosensitivity of the tumoral tissue and vary with respect to a normal tissue tolerance for early and late reactions. The results are described for several fractionation examples. It is shown that, within the tolerance limits of normal tissue, a greater tumor remission is achieved by hyper-fractionated irradiation than by a small number of high-dose irradiations.