Quantitative Analysis of Acute Adverse Radiation Effects and Flow of Large Arteriovenous Malformations After Stereotactic Radiosurgery

Introduction: Stereotactic Radiosurgery (SRS) of large arteriovenous malformations is associated with a high incidence of adverse radiation effects (ARE). To date, volume and dose-response models have been used to predict such effects. In order to understand radiosurgical ablation and its hemodynamic effects, we studied response flow analysis based on transit times and vessel diameters.

Methods: A retrospective analysis was conducted at a single institution using a prospective registry of patients managed between 2014 and 2020. We included AVM patients with a nidus larger than 5 cc who received either single session or volume-staged Gamma Knife radiosurgery with a minimum of two years of imaging follow-up. In total, 25 patients were included. AVM volume changes, volumes of parenchymal response, and obliteration were analyzed and correlated with transit times and diameters of feeding arteries and draining veins.

Results: Twenty-five patients included 15 women (60%). The average AVM volume was 12.6 cc (5.5-23). AVM locations were predominantly lobar (80%), and 17 (68%) were in critical locations. The mean margin dose was 17.2 Gy (15-21), and the median V12Gy was 25.5 cc. Fourteen (56%) AVMs had a transit time shorter than 1 second, and 11 had a longer transit time. The median VA ratio (sum diameter of the veins/sum diameter of feeding arteries) was 1.63 range (0.60-4.19). Complete obliteration was achieved in 13 (52%) at a median time of 41 months. Asymptomatic parenchymal effects were detected in 13 patients (52%), and were symptomatic in 4 patients (16%). The median time to ARE was 12 months (CI 95%7.6-16.4). On univariate analysis, significant predictors of ARE were VA ratio (p=0.024), transit time (p=.05), mean dose (p=0.028), and D95 (p=0.036).

Conclusion : Transit times and vessel diameters are valuable predictors of the subsequent parenchymal response following SRS. A more quantitative understanding of blood flow to an AVM is critical for predicting AREs.