Radiobiological rationale for stereotactic hypofractionated radiosurgery Part II. Normal tissue tolerance — dose constraints

Abstract

The response of normal tissues/organs to SHRS is more complex than to conventional radiotherapy. Tolerance doses TD5/5 and TD50/5, proposed by Rubin and Casarett, cannot be simply used for SHRS. Instead of LQED2, the BED is advised. The term risk dose (RD) corresponds better than TD to the risk of late morphological and functional disorders (OAR). BED doses show a rapid gradient with increasing distance of the OAR from the tumour GTV. Other risk factors include the dose-volume relationship, OAR organization (serial or parallel) and the ratio of the FSU to the target call. Vasculoendothelial cell damage initiates series of processes resulting in clinical and functional late effect. Using available data and studies, RDmin and RDmax for doses are listed as physical and BED doses for various OAR and dose-volume constraints. The RD values and constraints are rough estimates, since the available SHRS data are sparse and fragmentary, which should be interpreted cautiously and need further clinical validation.