Abstract
BACKGROUND: A single centre retrospective review of outcomes following linear accelerator - based stereotactic radiosurgery (SRS) for patients with 6 to 18 brain metastases was conducted. METHODS: Patients receiving SRS to multiple metastatic sites were identified from our institutional database and subsequently stratified into those with 6-9 metastases (group 1) and 10 or more metastases (group 2). RESULTS: 45 patients were evaluated in total with a mean number of metastases of 7 for group 1 and 14 for group 2. Mean total GTV volumes for each SRS treatment were 1.92cc (group 1) and 2.70cc (group 2). Median overall survival was 8 months for group 1 (0 -51 months) and 7 months (3-36 months) for group 2 . Following SRS, median time to intracranial progression was 3 months for both groups, occurring in 59% and 64% of group 1 and group 2 patients respectively. Following relapse, more patients in group 2 received whole brain/posterior fossa radiotherapy rather than SRS when compared with those in group 1 (80% vs 40%). The majority of patients surviving more than 1 year following SRS for ≥6 brain metastases had a targetable mutation (defined as any of ALK/EGFR/ROS1/BRAF mutation, ER+, HER 2+, PDL1 expression ≥ 1) in their primary tumour; 75% of group 1 and 100% of group 2. CONCLUSIONS: Although this study represents small patient numbers, we show that long term survival can be achieved for some patients following SRS for more than 5 brain metastases. However, many patients with more than 10 brain metastases develop intracranial relapse shortly after SRS and require whole brain/posterior fossa radiotherapy, indicating these patients are less likely to benefit from SRS. The presence of a targetable mutation in the primary tumour may indicate a better outcome following SRS for more than 5 brain metastases and warrants further investigation.