Single Institute Cohort Study on Multifraction Gamma Knife Radiosurgery for Intracranial Meningiomas: Efficacy and Risk Factors to Avoid Adverse Events.

BACKGROUND AND OBJECTIVES: – Multifraction Gamma Knife Radiosurgery (mf-GKRS) was introduced in the clinical practice over the past 20 years, but limited data exist about the effective radiation tolerance for these fractionated high-dose treatments. Our current aim was to report a single-institute long-term experience adopting mf-GKRS, focusing on any potential adverse effect. METHODS: – Retrospective observational cohort study on 216 perioptic and/or large (>10.0 cm3) meningiomas. Radiation was delivered over 3 consecutive days with Leksell G-frame. Upfront mf-GKRS was performed in 141 meningiomas (65.3%), whereas 75 (34.7%) underwent mf-GKRS as adjuvant or salvage therapy. The median follow-up was 62.0 months (IQR 43.0-85.0). RESULTS: – The baseline median tumor volume was 5.9 cm3 (IQR 2.2-11.0), and it was >10.0 cm3 in 65 cases (30.1%). The 5-year and 10-year clinical tumor control was 96.0% (CI 97.6%-94.4%) and 87.4% (CI 91.5%-83.3%), respectively. Cox regression demonstrated that up-front radiosurgery was the only independent predictor for better clinical tumor control (P = .011). Clinical outcome was stable or improved in 168 patients (77.8%) and transiently worse in 48 (22.2%), but the early and late rate of adverse radio-induced events with toxicity grade 3-4 was 2.8%. The risk of cranial nerve neuropathies (12.0%) remains higher in tumors larger than 10.0 cm3 (P = .019), despite hypofractionation. No cases of blindness occurred after mf-GKRS but optic neuropathy, new or worsening of preexisting one, developed in 7.9% cases: pretreatment visual decline (P = .008) and daily dose to 1 mm3 of anterior visual pathways ≥6.7 Gy (P = .011) were risk factors. Post-treatment edema (3.2%) was associated with higher gradient index (P = .008). CONCLUSION: – Mf-GKRS is effective and safe in perioptic meningiomas, representing a valid alternative to conventionally fractionated radiotherapy, adopting the limit of 6.7 Gy per fraction to 1 mm3 of anterior visual pathways, whereas it could be used with caution for large skull base meningiomas.