Response of Treatment-Naive Brain Metastases to Stereotactic Radiosurgery

Abstract With improvements in survival for patients with metastatic cancer, long-term local control of brain metastases has become an increasingly important clinical priority. While consensus guidelines recommend surgery followed by stereotactic radiosurgery (SRS) for lesions >3cm, smaller lesions (≤3cm) undergo SRS alone with variable responses. To determine factors influencing this variable response to SRS, we analyzed outcomes of brain metastases ≤3cm diameter in patients with no prior systemic therapy treated with frame-based single-fraction SRS. Following SRS, 294/1739 treated lesions demonstrated MRI findings concerning for local treatment failure (LTF), of which 228 /1739 (13%) demonstrated LTF and 66/1739 (3.7%) had an adverse radiation effect. Multivariate analysis demonstrated tumor size (>2cm) and melanoma histology were associated with higher LTF rates. Brain metastases ≤3cm are not uniformly responsive to SRS. Formal guidelines incorporating tumor size and histology are needed for determining whether to treat brain metastasis ≤3cm with SRS alone or surgery and SRS.