Intracranial arteriovenous malformations treated with LINAC-based conformal radiosurgery:: validation of the radiosurgery-based arteriovenous malformation score as a predictor of outcome

Objective: To validate the radiosurgery-based arteriovenous malformation score (RBAS) as a predictor of outcome in patients with arteriovenous malformations (AVMs) treated with LINAC-based conformal radiosurgery. Methods: We analysed 40 patients with a mean follow-up of 22 months. One patient (2.5%) pertained to Spetzler-Martin Grade I, 11 (27.5%) to Grade II, 19 (47.5%) to Grade III, eight (20%) to Grade IV and one (2.5%) to grade V. The mean RBAS was 2.0 (range: 0.76 - 5.56). The mean obliteration prediction index (OPI) and the Karlsson index (KI) were 0.74 ( range: 0.2 - 2.86) and 109.48 (range: 3.0 - 350.7) respectively. Outcomes were analysed according to the OPI, KI and RBAS. Results: We analysed different cutoff points in the RBAS and found a significant difference to predict the outcome in four scores: 1.2, 1.6, 1.7 and 1.8. In the group with RBAS <= 1.8, 13 (68%) had an excellent outcome and six (33%) did not, while with RBAS > 1.8, seven (32%) had an excellent outcome and 14 (67%) did not (p = 0.02). We did not find any correlation between Spetzler - Martin grading scale or OPI and outcome (p = 0.7 and p = 0.3 respectively). The KI predicted the excellent outcome in 8/9 patients (89%) with KI <= 27 and in 12/31 patients (39%) with KI >27 (p = 0.08). Conclusion: The RBAS seems to be a good predictor of outcome in patients with AVMs treated with LINAC-based conformal radiosurgery as in patients treated with Gamma Knife. It remains only to find the best cutoff point based on a larger series and longer follow-up.