Brainstem metastases treated with stereotactic radiosurgery: safety, efficacy, and dose response

The safety and efficacy of stereotactic radiosurgery (SRS) in the brainstem is questioned by some over concern of violating historical brainstem SRS dose tolerance. Our purpose was to report on the clinical outcomes of patients treated at our institution with radiosurgery for brainstem metastases. Patients with metastatic tumors within or directly abutting the brainstem from 1992 to 2014 were analyzed. Patient and tumor characteristics, SRS parameters, and toxicity were recorded and analyzed for associations with local control and survival. Multivariate statistical analysis was performed using Cox proportional hazards modeling. One-hundred and eighty-nine (189) brainstem metastases from 161 patients were included in our analysis. Whole brain irradiation was administered prior to SRS in 52 % of patients. The median margin dose was 18 Gy prescribed to the 50 % isodose line. Median imaging follow up was 5.4 months and median survival was 5.5 months after SRS. At last follow up, local control was achieved in 87.3 % of brainstem lesions treated. There were 3 recorded events of grade 3-5 toxicity (1.8 %). On multivariate analysis, a margin dose ≥16 Gy was associated with improved local control (p = 0.049) and greater KPS score was associated with improved overall survival following SRS (p = 0.024). Patients with brainstem metastases who have limited intracranial disease and/or who have received whole brain irradiation should be considered for SRS. Margin doses of at least 16 Gy are associated with superior local control, and serious radiation toxicity in SRS for brainstem metastasis appears rare.