Fractionated stereotactic radiotherapy with the Leksell Gamma Knife: feasibility study.

The main aim of this study was to check feasibility of stereotactic radiotherapy, which is routinely practised on linear accelerators, using a fixed Leksell stereotactic frame and a Leksell Gamma Knife. The study refers to the first experiences with 48 patients treated by a fractionated regimen (in 2-6 days). Isoeffect relationships calculations based on the linear-quadratic model and the levels of applied radiation doses, taking into account radiobiology of the tumour, tumour volume, critical structures surrounding the treated lesion and other factors are discussed. The procedure for quality control during the whole fractionated regimen is described. The study has shown that stereotactic radiotherapy with the Leksell Gamma Knife is feasible. However, only early effects can be discussed and there are still questions remaining which should be carefully studied: tolerance doses for critical structures at fractionation, definition of an 'ideal' fractionation regimen, and justification of the linear-quadratic model in the case of stereotactic radiotherapy.