INTERIM-REPORT ON THE RADIOSURGICAL TREATMENT OF CEREBRAL ARTERIOVENOUS-MALFORMATIONS - THE INFLUENCE OF SIZE, DOSE, TIME, AND TECHNICAL FACTORS ON OBLITERATION RATE

During the authors' initial 4-year experience with radiosurgery using the Leksell cobalt-60 gamma unit, they treated 121 patients with cereb ral arteriovenous malformations (AVMs). The radiosurgical dose to the margin of the nidus was 20 Gy for lesions less than 2.0 cm in diameter (volume less than or equal to 4.2 cm(3)); 18 Gy for malformations 2.1 to 3.0 cm in diameter (volume 4.2-14.1 cm(3)); and 16 Gy for malforma tions greater than 3.0 cm (volume > 14.1 cm(3)). Fifty-one patients un derwent follow-up angiography between I and 3 years after treatment, a nd complete obliteration of the nidus was confirmed in 38 (74.5%) of t hese patients. Thirty-two (74.4%) of 43 AVMs with volumes of 10 cm(3) or less and six (75%) of eight larger AVMs (volume 11-30 cm(3)) showed complete obliteration. Analysis of the time course of AVM nidus shrin kage and obliteration showed that most of the radiosurgically induced effect had occurred by 36 months after treatment. Retrospective analys is of the dose plans for 10 AVMs that were not obliterated by 36 month s after gamma knife radiosurgery at the authors' institution (eight ca ses) or elsewhere (two cases) revealed that six AVMs had not been cove red completely by the prescribed isodose. Six (5%) of the 121 patients developed neurological deficits as a direct result of radiosurgical t reatment. The authors infer from these data that malformations up to 3 0 cm(3) in volume (approximately 4.0 cm in average diameter) can be tr eated effectively with an acceptably low complication rate using a rad iosurgical dose of 16 Gy to the margin of the nidus. The obliteration rate for the larger malformations that were treated with a dose of 16 to Is Gy appears to be similar to that for smaller ones treated with 1 8 to 20 Gy. As more experience accrues using radiosurgery to treat AVM s, patient selection criteria and the variables associated with succes sful obliteration of the nidus should become more clearly defined.