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.

[Implementation of stereotactic focal radiotherapy using 10 MV x-ray].

Stereotactic focal irradiation is also called stereotactic radiosurgery by some neurosurgeons. This irradiation is used for the treatment of brain AVM (arterio-venous malformation) and small tumor. Application of stereotactic focal irradiation was developed with CRW (Cosman-Roberts-Wells) stereotactic device and two dimensional (2D) computer treatment planning system using 10 MV x-ray from a linear accelerator. This process of irradiation includes: (a) Identification and localization of a target volume in CRW stereotactic frame by CT scan or angiography. (b) To verify the alignment, a linear accelerator was used as a simulator to take portal films in anterior and lateral views. This was done to ascertain the angles between arc therapy, to encompass the target volume, and to exclude the critical organs such as lens at 0 degrees, 45 degrees, 90 degrees and 315 degrees couch angles. (c) A 2D computer treatment planning system was used to generate an isodose curve distribution for each couch angle. Then this was used to calculate the monitor unit per degree for rotation treatment. (d) 10 MV x-ray was used to implement the stereotactic focal radiotherapy.