[Radiology of radiosurgery]

Proper understanding of the fundamentals of radiosurgery and the main principles of radiobiology is a key point for the development and adaptation of therapeutic strategies and for the definition of indications. The prediction of local effects of radiosurgery requires taking into account both the target Volume and the marginal dose (energy,...) and not only the marginal dose which alone is poorly predictive of the outcome. Other additional factors such as topography, age, previous irradiations,... are likely to influence this risk relationship. The comparison of different dose regimens leads to proposing theoretical models for calculating radiobiological equivalences: the Biological Equivalent Dose (BED) Using these models one can think in terms of the practical consequences of dose fractionation. This allows, depending on the medical context, identifying the potential advantages of the radiosurgery or of a fractionated regimen. For small mid-sized vestibular schwannomas this approach indicates a clear advantage for a single-dose regimen. Retrospectively it has been possible to identify the dose-Volume relationship to the risk of neuropathy for facial motor function, facial sensitivity, and hearing.