Radiobiophysical aspects of stereotaxic radiation treatment of central nervous system diseases

The biophysical aspects of stereotaxic treatment are summarized, emphasizing the complex interplay between time-dose-fractionation, partial volume effect, physical dose distribution, and set-up uncertainties in influencing treatment outcome. The radiobiological advantage of dose-fractionation for normal tissue sparing is estimated using the linear-quadratic model and viewed in the context of clinical situations and results. Counterbalancing this benefit is the larger geometrical uncertainty associated with multiple fraction treatment, which would require increased treatment volume and an associated decrease in treatment dose. This last consideration requires knowledge of volume-dose relation of radiation-induced normal brain toxicity, the current status of which is also outlined.