SINGLE-FRACTION STEREOTACTIC RADIOTHERAPY - A DOSE-RESPONSE ANALYSIS OF ARTERIOVENOUS MALFORMATION OBLITERATION

Purpose: Stereotactic radiotherapy delivered in a high-dose single fra ction is an effective technique to obliterate intracranial arterioveno us malformations (AVM). To attempt to analyze the relationships betwee n dose, volume, and obliteration rates, me studied a group of patients treated using single-isocenter treatment plans. Methods and Materials : From Mag 1986 to December 1989, 100 consecutive patients with angiog raphically proven AVM had stereotactic radiotherapy delivered as a hig h-dose single fraction using a single-isocenter technique. Distributio n according to Spetzler-Martin grade was as follows: 79 grade 1-3, thr ee grade 4, 0 grade 5, and 18 grade 6. The target volume was spheroid in 74 cases, ellipsoid in II, and large and irregular in 15. The targe ted volume of the nidus was estimated using two-dimensional stereotact ic angiographic data and, calculated as an ovoid-shaped lesion, was 19 00 +/- 230 mm(3) (median 968 mm(3); range 62-11, 250 mm(3)). The mean minimum target dose (D-min) was 19 +/- 0.6 Gy (median 20 Gy; range: 3- 31.5). The mean volume within the isodose which corresponded to the mi nimum target dose was 2500 +/- 300 mm(3) (median 1200 mm(3); range 75- 14 900 mm(3)). The mean maximum dose (D-max) was 34.5 +/- 0.5 Gy (medi an 35 Gy; range 15-45). The mean angiographic follow-up was 42 +/- 2.3 months (median 37.5; range 7-117). Results: The absolute obliteration rate was 51%. The 5-year actuarial obliteration rate was 62.5 +/- 7%. After univariate analysis, AVM obliteration was influenced by previou s surgery (p = 0.0007), D-min by steps of 5 Gy (p = 0.005), targeted v olume of the nidus (less than or equal to 968 mm(3) vs. >968 mm(3); p = 0.015), and grade according to Spetzler-Martin (grade 1-3 vs. grade 4-6; p = 0.011). After multivariate analysis, the independent factors influencing AVM obliteration were the D-min [relative risk (RR) 1.9; 9 5% confidence interval (CI) 1.4-2.5; p < 0.0001] and grade distributio n according to Spetzler-Martin (RR 1.4; 95% CI 1.1-1.7; p = 0.010). De layed complications were observed in eight patients. The 5-year actuar ial rate of delayed complications was 7.4%. Conclusion: After stereota ctic radiotherapy delivered in a single high dose using a single-isoce nter technique, the success rate for complete obliteration is independ ently correlated to D-min but does not seem to be influenced by D-max and the targeted volume of the nidus. (C) 1998 Elsevier Science Inc.