Stereotactic radiosurgery for tectal low-grade gliomas

We report 7 cases with low-grade gliomas in the tectal region of the midbrain. This series started in 1979 and all tumors were treated by radiosurgery using the Leksell Gamma Knife. All cases were treated by using a single isocenter with the 14 mm collimator. Doses administered ranged from 14 to 35 Gy delivered to the 50-70% isodose line. All tumours but one responded to the treatment and disappeared or ceased growing. In the first two treated cases, the dose was chosen by the early experience from the AVM's, with 30 and 35 Gy as the peripheral dose. These cases developed severe radio-induced oedema with aggravating symptoms and permanent deficits. We conclude that radiosurgery is effective in the treatment of deeply located low-grade gliomas. Cases accepted for treatment should be carefully selected and the peripheral dose should not exceed 14Gy to avoid uncontrolled radio-induced changes.