PREDICTION OF OBLITERATION AFTER GAMMA-KNIFE SURGERY FOR CEREBRAL ARTERIOVENOUS-MALFORMATIONS

OBJECTIVE: To define the factors of importance for the obliteration of cerebral arteriovenous malformations (AVMs), thus making a prediction of the probability for obliteration possible. METHODS: In 945 AVMs of a series of 1319 patients treated with the gamma knife during 1970 to 1990, the relationship between patient, AVMs, and treatment parameter s on the one hand and the obliteration of the nidus on the other was a nalyzed. RESULTS: The obliteration rate increased both with increased minimum (lowest periphery) and average dose and decreased with increas ed AVM volume. The minimum dose to the AVMs was the decisive dose fact or for the treatment result. The higher the minimum dose, the higher t he chance for total obliteration. The curve illustrating this relation increased logarithmically to a value of 87%. A higher average dose sh ortened the latency to AVM obliteration. For the obliterated cases, th e larger the malformation, the lower the minimum dose used. This promp ted us to relate the obliteration rate to the product minimum dose (AV M volume)(1/3) (K index). The obliteration rate increased linearly wit h the K index up to a value of approximately 27, and for higher K valu es, the obliteration rate had a constant value of approximately 80%. F or the group of 273 cases treated with a minimum dose of at least 25 G y, the obliteration rate at the study end point (defined as 2-yr laten cy) was 80% (95% confidence interval = 75-85%). If obliterations that occurred beyond the end point are included, the obliteration rate incr eased to 85% (81-89%). CONCLUSION: The probability of obliteration of AVMs after gamma knife surgery is related both to the lowest dose to t he AVMs and the AVM volume, and it can be predicted using the K index.