Stereotactic radiosurgery for patients with 5 or more brain metastases: Retrospective single-institution analysis with focus on brain metastasis velocity

Purpose We describe patient outcomes following linear accelerator-based stereotactic radiosurgery (SRS) for ≥ 5 brain metastases, without prior or planned whole-brain radiotherapy. Methods We identified 116 eligible patients treated with SRS, from 2019–2024, for newly diagnosed brain metastases. We describe clinical factors associated with survival ≤ 2 months and analyze brain metastasis velocity measured as number (BMV) or volume (vBMV) of new metastases per year. Results The number of treated brain metastases ranged from 5–41 (median 10); net lesion volume ranged from 0.1–59.8 (median 5.2) cc. Primary cancers included non-small cell lung (n = 65), melanoma (n = 20), breast (n = 19), kidney (n = 6), gastrointestinal (n = 4), and other (n = 4) cancers. The 6-, 12- and 24-month overall survivals (OS) were 60.3%, 40.5%, 28.0%, respectively. Progressive extracranial disease at time of brain metastases and lower predicted survival from grade prognostic assessments were significantly adverse factors for OS on multivariable Cox regression, and were associated with ‘poor survivors’ who died ≤ 2 months from SRS (n = 21) or at > 2 months but opting against post-SRS cancer care and follow-up imaging (n = 6; OS = 2.1–5.8 months). Forty-two patients developed new brain metastases after SRS, while 28 (after ≥ 6-months follow-up) did not. Among these patients, OS was significantly associated with BMV and vBMV, though vBMV was not significant on multivariable Cox regressions that included BMV. Conclusions For patients with ≥ 5 brain metastases, clinical factors can potentially aid in selecting patients best-suited for SRS for multiple brain metastases, versus potentially deferring SRS in favor of supportive care. While vBMV is associated with OS, BMV appears more prognostic.