Long term survivors of stereotactic radiosurgery for brain metastases: do distant brain failures reach a plateau and what factors are associated with a brain metastasis velocity of zero?

Abstract

Life expectancy continues to increase for patients with brain metastases treated with stereotactic radiosurgery (SRS). The present study sought to retrospectively analyze brain metastasis patients who have survived 2years or more, and assess for what factors may predict for a final brain metastasis velocity (BMV) of zero. This was a single-institution retrospective study of 300 patients treated with SRS from 2001 to 2019 for brain metastases who survived greater than 2years after first SRS. Final BMV is calculated by summing all metastases through the observed time divided by the total time in years. A BMV of zero is defined as at least 2years of imaging follow-up without distant brain failure (DBF). Median age at first SRS is 61 (IQR: 53, 70). Kaplan-Meier estimated median overall survival is 4.9years and time to DBF is 1.5years (95% CI 1.2, 2.0). Twenty-eight (9.3%) patients underwent subsequent WBRT. One hundred and one (33.7%) patients never had any further brain metastases (BMV = 0) at a median follow-up time of 3.3years. Median BMV is 0.4 (IQR: 0, 1.4). Distant brain failures reach a plateau at 4years where the cumulative incidence of DBF is 82%. 70% of first time DBFs have occurred by 2years. Factors significantly associated with a BMV of zero include fewer brain metastases at first SRS (HR 1.1; p = 0.0004) and Caucasian race (HR 1.5; p = 0.03). Approximately one third of brain metastasis patients who live beyond 2years after initial SRS have a BMV of zero. DBFs appear to reach a plateau at 4years. Factors significantly associated with a BMV of zero include Caucasian race and having had a single brain metastasis at first SRS.