Single Fraction and Fractionated Radiosurgery for Treatment of Brainstem Metastases

Stereotactic Radiosurgery (SRS) is a standard of care for the treatment of patients with a limited number of brain metastases. SRS has also been increasingly utilized for metastatic lesions involving the brainstem given that surgical resection is not feasible and the devastating consequences of local progression in this area. However, data on the safety, efficacy, and doses is limited to small, retrospective series and is mostly constrained to SRS delivered in a single fraction (SF-SRS). Multi-fraction SRS (MF-SRS) is an attractive option for brainstem metastases due to the potential therapeutic gain given the target being located within a critical structure. The purpose of this study was to evaluate local control (LC) and radiation necrosis (RN) in a series of patients treated with SF-SRS or MF-SRS for brain metastases and to compare the outcomes between these two groups. Patients treated at a single institution between 2003-2017 with SF-SRS or MF-SRS for lesions within the brainstem were retrospectively collected. All SRS was performed with either sterotactic radiosurgery or robotic radiosurgery. Kaplan-Meier method was used to evaluate LC, RN, and overall survival (OS), and comparisons between groups were evaluated using the log rank test. Chi-square and independent t-test were used to assess for clinical factors and correlations between the two groups. A total of 25 patients treated with SRS to 27 brainstem lesions were identified, 12 patients treated with SF-SRS and 13 treated with MF-SRS. Median follow-up was 6.4 months. Median tumor volume was 0.27 mL. A total of 88.9% of patients had additional CNS lesions treated with SRS at the time of brainstem SRS. Median dose was 16 Gy (15-18 Gy) with SF-SRS and 24 Gy (18-30 Gy) with MF-SRS. Median number of fractions in the MF-SRS was 3 (3-5). Patients treated with MF-SRS were on average younger (mean age 65 vs. 57, p=0.048) and had larger mean tumor volumes (.340 vs 0.947 mL, p=0.010). OS was 78.7% at 6 months and 58.3% at 12 months. There was no difference in LC between SF-SRS and MF-SRS at 6 months (100% vs 88.9%, p=0.157) or 12 months (50.0% and 74.1%, p=0.991). There was a single case of RN that occurred 102 days after MF-SRS (30 Gy in 5 fraction) which was confirmed by MR spectroscopy. All cases of LF and RN were symptomatic. Predictors for LF at 6 months were receipt of prior WBRT (RR-10.8, p=0.015) and tumor volume >0.5 mL (p=0.013). There were no failures in tumors <0.5 mL at 6 months. No other clinical factors were associated with LC or RN. SF-SRS and MF-SRS are effective treatments for brainstem metastases, especially for small targets. In this small cohort, there was no difference in outcomes comparing SF-SRS and MF-SRS.