2026 Proffered Presentations
S133: IMPACT OF TIMING OF ADJUVANT RADIOTHERAPY ON TUMOR CONTROL FOLLOWING SUBTOTAL RESECTION OF VESTIBULAR SCHWANNOMAS
Rithvik Ramesh, BA1; Lourdes Kaufman, BA1; Ruben Hernandez, BS1; Stephanie Younan, BS, MPH1; Nadeem Al-Adli, MD2; Philip V Theodosopoulos, MD1; Steven W Cheung, MD1; Nicole T Jiam, MD1; Ramin A Morshed, MD1; 1University of California, San Francisco; 2University of North Carolina at Chapel Hill
Introduction: One approach to the management of vestibular schwannomas is to perform subtotal tumor resection (STR) and treat the residual tumor with stereotactic radiosurgery (SRS), either within months or in a delayed manner once tumor progression is observed on imaging. Critically, it remains unclear whether the timing of SRS following surgery affects tumor control. Therefore, we explored the impact of early versus delayed postoperative SRS on long-term recurrence risk.
Methods: Retrospective chart review identified patients who underwent STR and subsequent SRS for newly diagnosed vestibular schwannomas between 2004 and 2024 at a large urban tertiary care center. Early SRS was defined as treatment within 1 year postoperatively while delayed SRS was treatment after 1 year. Recurrence was defined as radiological evidence of interval growth of the residual tumor on serial MRI. Preoperative and postoperative tumor volumes were determined with manual tumor segmentation. Demographic, clinical, and tumor characteristics were described and compared between early and delayed groups using appropriate parametric and non-parametric statistical tests. Kaplan-Meier survival curves with log-rank tests were used to assess differences in recurrence-free survival (RFS) based on timing of SRS.
Results: Our final analytic cohort included 164 patients with subtotally resected vestibular schwannomas, with a mean age of 50.3 years (SD 14.6 years) and a slight female predominance (N=91; 55.5%). Most patients received early SRS (N=137; 83.5%), averaging 5.8 months (SD 2.2 months) postoperatively. The remainder of patients underwent delayed SRS (N=27; 16.5%) after a mean period of 20.8 months (SD 9.6 months). Mean preoperative tumor volume was 11.4 cm3 (SD 8.5 cm3) in the early SRS group and 14.4 cm3 (SD 11.3 cm3) in the delayed SRS group (p=0.353). Mean postoperative tumor volume was 2.5 cm3 (SD 3.0 cm3) in the early SRS and 3.2 cm3 (SD 3.9 cm3) in the delayed SRS group (p=0.796). Tumor growth prior to SRS was more common in the delayed SRS group (51.9% vs 7.3%; p<0.001), however rates of recurrence did not vary significantly based on SRS timing (4.4% vs 0.0%; p=0.591) over average post-SRS follow up durations of 3.6 years (SD 3.2 years) for the early SRS group and 3.2 years (SD 2.8 years) for the delayed SRS group (p=0.736). RFS also did not vary significantly between groups; 5-year recurrence risks were 0.0% and 4.5% in the early and delayed SRS groups while 10-year risks 0.0% and 24.1% (p=0.171).
Conclusions: Timing of postoperative SRS after subtotal resection of vestibular schwannomas was not associated with significant differences in recurrence-free survival, although patients in the delayed treatment group experienced higher rates of interval tumor growth prior to SRS. Given the small, selected nature of the delayed cohort, long-term outcomes remain uncertain, and trends suggest a potentially higher and clinically meaningful 10-year recurrence in this group. These results indicate that deferring SRS until radiographic progression may be reasonable for carefully selected patients, but longer follow-up is needed to fully assess the impact on long-term tumor control.
