Implementation of stereotactic focal radiotherapy for intracranial arteriovenous malformations using a linear accelerator.

A system of stereotactic focal radiotherapy using a linear accelerator has been developed in cooperation with a neurosurgeon. The treatment is delivered using a carefully calibrated 10 MV machine and the Cosman-Roberts-Wells (CRW) system. The precision of the method as well as its quality assurance is described. Eight patients with intracranial arteriovenous malformations (AVM) received irradiation from August 1990 to November 1991. The prescribed dose at the periphery of the AVM was 8 Gy per session, with six patients receiving two sessions and two patients receiving one session. The field size, encompassing the 90% isodose, ranged from 20 mm to 35 mm. In four patients, follow-up angiography was performed one year after the full course of therapy; total obliteration of the AVM was noted in three (75%) with a partial response in the other. In the other four patients, follow-up angiography was not performed; one patient, who had only one session of irradiation, experienced rebleeding six months later and died, and the other three patients had no further episodes of bleeding during their follow-up of 28, 18 and 14 months, respectively. Linear accelerator-based stereotactic focal radiotherapy can attain a precisely defined and reproducible dose distribution. The effects of this treatment may take one to two years to develop. Our preliminary study suggests that it is an effective alternative treatment for surgically inaccessible lesions. Patients with a small cavernous sinus dural AVM appear to have a better and more rapid response.