On the problem of the characterization of late effects by a linear-quadratic survival function. I. Theoretical and radiobiological aspects.

Radiobiological data have been used for an analysis of acute and late tissue responses on the basis of a linear-quadratic survival function SLQ = exp(-alpha d -beta d2). Isoeffect curves of late effects exhibit a steeper slope than those for the corresponding acute effects, and, therefore, late effects may become an essential aspect in the radiotherapy of many kinds of tumours. In this communication, the theoretical and radiobiological view will be presented, whereas in a second part clinical applications will play a dominant role: Thus a statistical analysis of clinical observations has revealed that the volume factor of the irradiated tissue represents an important factor with regard to the characteristic average latency period, when clinical effects will become manifested.