Single-Session Versus Hypofractionated Gamma Knife Radiosurgery for Large Parasagittal Meningiomas: A Retrospective...

Background/Objectives: Large parasagittal meningiomas (PSMs) present significant surgical challenges due to their proximity to the superior sagittal sinus, and the optimal radiosurgical strategy for large tumors remains debated. This study compared local control (LC) and treatment-related radiological and clinical outcomes after single-session (ss-GKRS) and hypofractionated (hf-GKRS) Gamma Knife radiosurgery in PSMs ≥8 cm³. Methods: Eighty-seven patients with 87 radiologically confirmed PSMs treated between April 2006 and February 2025 were reviewed. Patients with histopathologically confirmed atypical or anaplastic meningiomas or imaging features suspicious for higher-grade disease were excluded. Fifty-nine patients underwent ss-GKRS and 28 received hf-GKRS. The median tumor volume was 11.2 cm³ (range 8-37.8 cm³). LC was defined as tumor volume regression or stability on serial MRI. Radiological complications were defined as new or worsening peritumoral T2 hyperintensity, and clinical complications as new neurological symptoms. Time to local progression was compared using the log-rank test, with an exploratory volume cut point from ROC analysis. Results: The median follow-up was 62 months (range 12-186 months). Overall crude LC was 93.1%, including 89.8% (53/59) after ss-GKRS and 100% (28/28; exact 95% CI 87.7-100%) after hf-GKRS. All six local progressions occurred in the ss-GKRS group; however, freedom from local progression did not differ significantly between the groups (log-rank p = 0.137). In an exploratory volume-stratified analysis, LC was 100% in both groups for tumors ≤11.75 cm³. Among tumors >11.75 cm³, crude LC was 71.4% (15/21) after ss-GKRS and 100% (16/16) after hf-GKRS (Fisher exact p = 0.027). Post-treatment radiological edema occurred in 39.0% after ss-GKRS versus 25.0% after hf-GKRS (p = 0.235). Conclusions: Overall freedom from local progression did not differ significantly between ss-GKRS and hf-GKRS. No local failures were observed after hf-GKRS during its shorter available follow-up, including among tumors >11.75 cm³ in an exploratory analysis. These findings support hf-GKRS as a feasible treatment option for selected larger PSMs, but neither treatment superiority nor a definitive tumor-volume threshold can be established from this retrospective cohort.