Indications of stereotactic irradiation for brain lesions

Stereotactic radiosurgery (SRS: single-fraction stereotactic irradiation) w as originally developed to treat benign lesions in the brain, and has been adopted for the treatment of small primary or metastatic brain tumours. It has recently been recommended that stereotactic radiotherapy (SRT: fraction ated stereotactic irradiation) be applied to the treatment of brain tumours : however, it requires much more time and work than SRS, and sufficient rad iobiological evaluations of these techniques have never been carried out. B iologically effective doses were calculated to determine the indications fo r SRS and SRT, and to decide on an effective SRT schedule, incorporating th e factors of 'repair' and 'cell proliferation'. The results suggest that SR S would be recommended for arteriovenous malformations and benign tumours t hat have distinct margins separating them from surrounding normal tissue an d SRT would be recommended for benign or malignant brain tumours without cl early defined boundaries. The recommended SRT schedules would be 7 Gy x 7 f ractions every other day for malignant tumours and 3.5 Gy x 12 fractions ev ery other day for benign tumours. However, clinically, these schedules shou ld be modified according to many other factors in individual cases.