(808) Association Between Facility Case Volume and Postoperative Radiation After Surgery for Vestibular Schwannoma

Introduction: Higher facility case volume is well established to be associated with reduced complication rate in vestibular schwannoma (VS) surgery; however, its relationship with the adequacy of durable surgical tumor control has not been well characterized. Radiosurgery following surgery may serve as a pragmatic indicator of suboptimal care in a disease where single-modality treatment is often achievable. We hypothesize that patients treated at lower-volume facilities are more likely to undergo postoperative radiosurgery, reflecting differences in treatment adequacy.

Methods: Retrospective cohort study using the National Cancer Database (2004-2023). Patients with VS (site C724, histology 9560/9570) undergoing surgery were included. Treating facility surgical case volume was calculated as a 2-year rolling window. The primary outcome was any postoperative radiation therapy. We first examined the shape of the association between facility volume and postoperative radiation using restricted cubic splines. Based on this relationship, we constructed multivariable-adjusted logistic regression models examining the association between facility volume and postoperative radiation across distinct volume ranges, estimating separate linear effects within each range. Models were adjusted for age, sex, tumor size, race, insurance, income, and Charlson-Deyo comorbidity score.

Results: Among 16,400 patients who underwent VS surgery at 718 facilities, 804 (4.9%) received postoperative radiation. Median facility case volume was 16 cases per 2 years (IQR 6-36). We identified two volume thresholds at 16 and 60 cases/2 years. Below 16 cases, each additional case reduced radiation odds by 7.0% (OR=0.93 [95% CI 0.90-0.96]). Between 16 and 60 cases, facility volume was not associated with postoperative radiation (OR=1.00 [0.96, 1.04]). Above 60 cases, there was a non-significant reduced odds of radiation (OR=0.95 [0.87, 1.04]).

Conclusions: Higher facility VS surgical volume was associated with lower odds of postoperative radiation therapy, with 16 cases per 2 years representing a potential risk-defining threshold.