THE ROLE OF HIGH-DOSE, SINGLE-FRACTION IRRADIATION IN SMALL AND LARGEINTRACRANIAL ARTERIOVENOUS-MALFORMATIONS

Purpose: Radiosurgery with external beam irradiation is an accepted tr eatment for small intracranial vascular malformations. It has been pro ven effective and safe for lesions with volumes of less than 4 cc. How ever, there is only some limited clinical data for malformations of gr ade 4 and grade 5, according to Spetzler and Martin. Methods and Mater ials: At the Heidelberg radiosurgery facility equipped with a linear a ccelerator, 212 patients with cerebral arteriovenous malformations hav e been treated since 1984. Thirty-eight percent of the arteriovenous m alformations treated were classified inoperable, 14% grade 5, 19% grad e 4, and 29% grades 1-3. Radiation doses between 10 and 29 Gy were app lied to the 80% isodose contour. Results: Above a threshold dose of 18 Gy, the overall obliteration rate was 72%. After 3 years, the obliter ation rates were 83% with volumes of less than 4.2 cc, 75% with volume s of up to 33.5 cc, and 50% with volumes of up to 113 cc. Of the patie nts presenting with seizures and paresis, 83% and 56%, respectively, s howed improvement, which correlated with the degree of obliteration. A fter a follow-up period of up to 9 years, the rate of radiation-induce d severe late complications was 4.3%. In grade 5 lesions, the risk of side effects was 10%. No serious complications occurred if a maximum d ose of less than 25 Gy was applied to treatment volumes of less than 3 3.5 cc. Conclusion: The success of stereotactic high-dose irradiation of arteriovenous malformations depends on the dose applied. The incide nce of radiation-induced side effects increased with the applied dose and treatment volumes. From our experience, doses of less than 25 Gy a nd treatment volumes of up to 33.5 cc are safe and effective. In the f uture, new techniques of radiosurgery with linear accelerators and dyn amically reshaped beams will allow us to apply homogenous dose distrib utions. Additional use of magnetic resonance angiography for 3D treatm ent planning will help to identify the nidus more easily.