Stereotactic radiosurgery alone for patients with 16 or more brain metastases: Retrospective single-institution analysis

Objective

We sought to report outcomes of patients treated with linear accelerator-based stereotactic radiosurgery (SRS) alone (in one course) for 16+ brain metastases, without prior or planned whole-brain radiotherapy (WBRT).

Methods

We identified 29 eligible patients treated from 2019 to 2024, and retrospectively analyzed overall survival (OS) and cancer control outcomes. Twenty-eight underwent 3-fraction SRS (mostly 8–9 Gy per fraction), and 1 underwent single-fraction SRS (20 Gy).

Results

Primary cancers included non-small cell lung (n = 14), breast (n = 5) and kidney (n = 1) cancers, and melanoma (n = 9). For those who had undergone prior SRS for <16 brain metastases (n = 9) versus those with newly diagnosed brain metastases (n = 20): 16–39 (median = 22) vs 16–41 (median = 26) brain metastases were treated; net lesion volumes were 0.2–10.0 (median = 2.0) vs 1.3–58.8 (median = 5.8) cc (p = 0.050); median OS was 19.8 vs 6.0 months (p = 0.47). Among all 29 patients, 10 underwent a second SRS for local recurrence (n = 2), new metastases (n = 7) or both (n = 1). Two underwent salvage WBRT, 1 received systemic therapy in lieu of WBRT and 4 developed intracranial disease progression not amenable to SRS (along with extracranial progression in 3) for whom WBRT was not consistent with their goals of care. One patient developed hemorrhagic transformation of a metastasis; no others experienced grade ≥3 late toxicity.

Conclusions

SRS-alone for 16+ brain metastases is well-tolerated in patients who, in general, experience poor OS. A multitude of factors confound assessment of potentially prognostic factors in our series. More study of SRS-alone for high-number multiple brain metastases is warranted.