Long-term treatment results of staged stereotactic radiosurgery for posterior fossa brain metastases with volume larger than 4 mL.

Abstract

Managing large posterior fossa brain metastases (PFBMs) poses significant challenges. Although staged stereotactic radiosurgery (SRS) is an effective and minimally invasive alternative for large brain metastases, its clinical utility for large PFBMs has not yet been fully elucidated. The aim of this study was to evaluate the safety and efficacy of staged SRS in the treatment of large PFBMs. This retrospective analysis included patients who underwent upfront staged SRS for PFBMs measuring 4 mL or larger between 2010 and 2024 at a single tertiary cancer center. Patients who had received prior local treatment were excluded from the study. The radiosurgical protocol encompassed delivering 24-30 Gy in 2 fractions, with a time interval of 3-4 weeks between sessions. Outcome measures, including overall survival, local control of large PFBMs, and leptomeningeal metastasis (LM), were assessed using time-dependent analyses, considering competing events when appropriate. A consecutive cohort of 92 patients (49 male, median age 68 years) with 96 large PFBMs was included in the study. Primary cancers were small cell lung cancer, non-small cell lung cancer, and colorectal, breast, genitourinary, and upper digestive tract cancers in 11, 30, 24, 16, 7, and 4 patients, respectively. Eighty-two patients (89%) exhibited neurological symptoms, and the median volume of large PFBMs was 9.0 mL. At the time of the second session, the median PFBM volume had decreased by 49% to 4.6 mL. During the treatment interval, 2 patients underwent urgent craniotomies due to tumor bleeding and obstructive hydrocephalus. The 1- and 2-year overall survival rates following staged SRS were 51% and 30%, respectively (median 12.2 months). The 1- and 2-year local failure rates for large PFBMs were 17% and 23%, respectively. Rapid tumor response (defined as a 50% or greater volume reduction at the second session) was the sole factor associated with higher probability of local tumor control (HR 0.32, 95% CI 0.12-0.86; p = 0.024). The mean Karnofsky Performance Status (KPS) score improved from 71 at the first SRS session to 85 at the second; the first follow-up mean KPS score was 90 (p < 0.001). The 1- and 2-year LM rates remained low at 11% and 14%, respectively. These results suggest that staged SRS is a safe and less invasive treatment option for selected patients with PFBMs larger than 4 mL, achieving reasonable local control rates and low LMs rates in the long term.