Radiobiological analysis of tissue responses following radiosurgery.

Stereotactic radiosurgery provided clinicians the ability to administer high single-doses of radiation to intracranial targets with relative safety. Analysis of clinical outcome from radiosurgery calls into question some of the radiobiological principles that have guided conventional fractionated radiotherapy in the past. The response of the tumor or target tissue being irradiated, as well as the response of the surrounding normal tissue, seems predominantly determined by the tumor or target vasculature. Injury to the tumor or target vasculature appears to contribute to the probability of developing normal tissue complications. Estimations of alpha/beta values from radiosurgical dose-response data consistently yield values that conflict with values from fractionated radiotherapy and with linear-quadratic theory. This indicates that projections from high-dose single-fractions to fractionated dose-equivalents made using the linear-quadratic formula are unreliable. Radiobiological analysis of clinical data from radiosurgery provides models for guiding treatment to achieve desired effects and provide reliable estimates of complications.