2603 - Evaluating Outcomes of Patients Receiving SRS to More Than 15 Brain Metastases in a 12-Month Span

Purpose/Objective(s): Randomized trials support treatment of up to 15 brain metastases in an initial course. Some insurers limit radiosurgery in a 12-month span to 15 metastases even though technical improvements in radiosurgery facilitate treating patients with greater than 15 metastases. Previously published data for up to 15 metastases at initial SRS shows overall survival (OS) in the 5-15 cohort was 7.5 months and salvage WBRT rate was 16%. The present study hypothesizes that treatment of >15 metastases would not worsen outcomes compared to WBRT with modern techniques.

Materials/Methods: Patients treated with SRS between January 2015 and May 2022 at a single institution were evaluated and any with more than 15 brain metastases in a 12-month span were selected. Patients were treated via linear accelerator based frameless single isocenter SRS using 1, 3, or 5 fractions as deemed appropriate by the treating physician. The first course (FC) group where those who were receiving their first course of brain SRS while the multiple course (MC) group included those who had received previous courses of SRS. Median OS and time to distant brain failure (DBF) for each group was calculated as well as percentage of patients receiving WBRT and additional SRS later. The Kaplan-Meier method was used to estimate OS and time to DBF and compared using the log rank test. Fisher’s exact test was used to evaluate differences in proportion of patients receiving WBRT and additional SRS.

Results: In total, 44 patients were identified with 16 or more metastases treated within a 12-month span or at time of first SRS course who would otherwise meet criteria for SRS treatment according to current insurance guidelines. Nineteen were in the FC group and 25 were in the MC group. The median OS for the FC group was 7.9 months and median time to DBF was 3.3 months. The MC group had a median OS of 10.5 months with a median time to DBF of 3.3 months. In the FC group 15.8% of patients received salvage WBRT and 15.8% received at least 1 additional course of SRS. No patients received both in this group. Conversely, 40% of patients received salvage WBRT and 40% received at least 1 additional course of SRS in the MC group. Three patients received an additional course of SRS prior to receiving WBRT. There was no significant difference between groups for percentage receiving WBRT or additional courses of SRS (p = 0.10 and p = 0.10, respectively). In the total cohort, 70% of patients avoided WBRT with SRS alone and only 7% received WBRT after SRS to >15 metastases. Neither OS nor time to DBF was significantly different between groups (p = 0.78 and p = 0.83, respectively).

Conclusion: Outcomes for patients being treated for more than 15 brain metastases appear similar to published results for patients with fewer metastases in both the initial and salvage SRS setting. Additional research is warranted to validate these results.