Analysis of Survival Outcomes of Patients Treated with Stereotactic Radiosurgery for High Volume Brain Metastases

Abstract

<h3>Purpose/Objective(s)</h3> To analyze outcomes and assess for factors associated with improved survival in patients with greater than or equal to 20 cumulative brain metastases treated with stereotactic radiosurgery (SRS). <h3>Materials/Methods</h3> This was a single institution, retrospective analysis that included patients with 20 or more cumulative brain metastases treated with SRS. Between December 2015 and February 2022, 96 patients were identified that met the inclusion criteria, and their clinical, tumor, and treatment data were used for analysis. Overall survival outcomes, defined as the time interval from initial SRS treatment until death from any cause, were calculated using the Kaplan-Meier method for various patient, tumor, and treatment factors. The log-rank test was used to compare subgroups and investigate patient characteristics for significance. <h3>Results</h3> The median follow-up time, defined as the interval between date of initial SRS and last recorded physician follow-up, was 8.7 months. Median ages at time of initial cancer diagnosis, initial brain metastases diagnosis, and initial SRS treatment were 60, 57 and 60 years, respectively. The most common primary tumor histologies were lung (48%) and breast (23%), followed by melanoma (10%), and renal cell carcinoma (8%), with the remaining 10% of patients being grouped together due to rare histology. In regard to treatment characteristics, the median cumulative number of brain metastases was 31.5 (range 20-158) with the median of 22 brain metastases treated in a single SRS treatment course. The majority of patients were treated with a distributed SRS technique (86%). The median number of cumulative SRS sessions was 2 (range 1-7). Median overall survival for the entire cohort was 12.6 months. Categorized by primary histology, the median OS for lung, breast, melanoma, RCC, and other was 14.8, 15.5, 8.9, 22.8, and 6.5 months, respectively (NS, p=0.182). Further analysis of factors associated with overall survival found the presence of a targetable mutation (18.4 vs 10.5 months (HR 0.48, 95% CI 0.29-0.78, p=0.004)) and not having received whole brain radiotherapy (15.5 vs 9.3 months (HR 1.92, 95% CI 1.11-3.33, p=0.008)) as significant predictors of overall survival. ECOG performance status at time of initial SRS (0-1 vs 2) was trending toward significance (13.6 vs 9.7 months (HR 0.93, 95% CI 0.54-1.62, p=0.068) but was not statistically relevant. <h3>Conclusion</h3> Treatment of high-volume brain metastases with SRS appears to be safe and is feasible in selected patient populations. Survival rates appear comparable to prospective studies utilizing upfront conventional whole brain and hippocampal sparing radiation. Further studies are needed to validate this approach and identify patients best suited for this treatment paradigm.