Upfront stereotactic radiosurgery for large posterior fossa metastases: a multicenter evaluation of clinical outcomes

Purpose: Management of large posterior fossa metastases is challenging due to proximity to critical neuroanatomical structures and the potential need for urgent surgical decompression. While surgical resection is traditionally favored for large or symptomatic lesions, the role of upfront stereotactic radiosurgery (SRS) remains incompletely defined. This study aims to evaluate the clinical, radiological, and survival outcomes of upfront SRS for large cerebellar metastases to assess its viability as a primary treatment. Methods: This retrospective, two-institution study (2007–2024) included 61 adults with large cerebellar metastases (volume ≥ 5 cm³). Primary outcomes were overall survival (OS), local control (LC), and subsequent neurosurgical intervention. Secondary outcomes included tumor volume reduction. Results: Mean tumor volume was 11.9 cm³. LC was achieved in 93% of evaluable patients. Median OS was 12.6 months, with estimated survival rates of 68%, 54%, and 43% at 6, 12, and 24 months, respectively. Significant tumor mass reduction occurred following SRS (mean decrease 6.16 cm³, p < 0.001). Only 5% of patients required post-treatment neurosurgery. On multivariable analysis, a greater number of treatment fractions was associated with improved survival, whereas higher total radiation dose was associated with worse survival. Conclusions: Upfront SRS for large posterior fossa metastases provides excellent LC, significant volume reduction, and favorable survival, while rarely necessitating subsequent surgical intervention. These findings suggest that, in carefully selected patients, SRS may serve as an effective primary treatment strategy that can obviate the need for surgical resection, even in large-volume posterior fossa disease.