Stereotactic radiosurgery of intracranial arteriovenous malformations and the use of the K index in determining treatment dose

Object. The appropriate dose during stereotactic radiosurgery (SRS) of cerebral arteriovenous malformations (AVMs) remains a matter of debate. In the present study, the authors retrospectively evaluated the association of using a prescribed dose calculated utilizing the K index with the obliteration rate of cerebral AVMs after SRS. Methods. The authors performed a retrospective analysis of the Cleveland Clinic SRS database. All patients undergoing Gamma Knife radiosurgery for cerebral AVMs from 1997 to 2010 were selected. Regression techniques and Kaplan-Meier analyses were used to investigate the effect of divergence from the optimal K index dose on the rate of AVM obliteration. Results. In the study period 152 patients (mean age 43.6 years; 53.9% of treatments were performed in females) underwent 165 Gamma Knife radiosurgery treatments for AVMs. In a univariate analysis Spetzler-Martin grade (OR 0.63 [95% CI 0.42-0.93]), higher AVM score (OR 0.43 [95% CI 0.27-0.70]), larger AVM volume (OR 0.88 [95% CI 0.82-0.94]), and higher maximum diameter (OR 0.56 [95% CI 0.41-0.77]) were associated with a lower rate of AVM obliteration. Higher margin dose (OR 1.16 [95% CI 1.08-1.24]) and higher maximum dose (OR 1.08 [95% CI 1.04-1.13]) were associated with a higher obliteration rate. To further examine the effect of prescribed dose divergence from the calculated K index dose, cases were classified to groups depending on the AVM volume and dose variance from the ideal K index dose. Contingency tables and Kaplan-Meier curves were then created, and no significant differences in rates of obliteration were noted among the different groups. Conclusions. Gamma Knife radiosurgery for cerebral AVMs remains an effective and safe treatment modality. Smaller AVMs may receive doses less than the calculated K index dose without an apparent effect on obliteration rates.