Safety and Effectiveness of Volumetric Modulated Arc Therapy-Based Stereotactic Radiosurgery for Posterior Fossa Brain Metastases: A Single-Centre Experience

<b>Background/Objectives:</b> Posterior fossa brain metastases (PFBMs) pose particular risks owing to their proximity to the brainstem and fourth ventricle. We evaluated the safety (treatment-related complications), local effectiveness, and procedural efficiency of volumetric modulated arc therapy (VMAT)-based stereotactic radiosurgery (VMAT-SRS) for PFBMs. <b>Methods</b>: This single-centre, retrospective study derived a PFBM subgroup from an overall institutional cohort of 123 patients treated with VMAT-RapidArc SRS/fSRS. The doses were 12-20 Gy (single fraction) or 5 × 6 Gy (selected cases). Local response (mRECIST) and predefined safety endpoints (symptomatic oedema with brainstem/IV-ventricle compromise, obstructive hydrocephalus, haemorrhagic transformation, CSF diversion, and urgent neurosurgery) were assessed. Overall survival and procedural time were analysed. <b>Results</b>: Thirty-one patients (39 lesions) were included; 76.9% of them received single-fraction SRS. In addition, 74.2% of patients had supratentorial metastases with posterior fossa involvement. Kaplan-Meier overall survival at 6, 12, 24, and 48 months was 74%, 58%, 26%, and 9.7%, respectively; the median survival time was 12.6 months. Among evaluable lesions, local control was 84.5% (per-lesion response: 15.5% PD, 28.1% SD, 34.4% PR, and 22.0% CR). No clinically significant posterior fossa local complications were observed. Three patients developed radiation-induced leukoencephalopathy after whole-brain radiotherapy (WBRT) and radiosurgery for synchronous supratentorial metastases. The median procedural time was 25.0 min (IQR 9.0) with one isocentre versus 52.5 min (IQR 9.75) with two. <b>Conclusions:</b> VMAT-SRS/fSRS for PFBMs achieved high local control, very low posterior fossa toxicity, and favourable procedural efficiency, supporting its use as a safe, rapid, frameless alternative to WBRT and other radiosurgical platforms such as Gamma Knife in appropriately selected patients.