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

<h3>Purpose/Objective(s)</h3> Life expectancy continues to increase for patients with brain metastases treated with stereotactic radiosurgery (SRS), and as such, questions regarding how long patients need surveillance imaging have become more relevant. The present study sought to retrospectively analyze brain metastasis patients who have survived two years or more, and assess for what factors may predict for a final brain metastasis velocity (BMV) of "zero." <h3>Materials/Methods</h3> This was a single-institution retrospective study of 300 patients treated with SRS from 2001 to 2019 for brain metastases without prior whole brain radiotherapy (WBRT) who survived greater than two years after first SRS. Clinical outcomes were determined via the Electronic Medical Record. 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 two years of imaging follow-up without distant brain failure (DBF). The cumulative incidence of DBF is via the Fine Gray Method and defined from time of first SRS to time of DBF. <h3>Results</h3> Of the 300 patients in this review, median age at first SRS is 61 (IQR: 53, 70). Primary cancers include lung cancer (50%), breast cancer (16%), melanoma (15%), GU primary (11%), GI primary (4%) and other (4%). Median number of metastases at first SRS is one (IQR: 1, 3). Median follow-up is three years (IQR: 2.3, 5.1). Kaplan-Meier estimated median overall survival is 4.9 years. In this patient population, the median Kaplan-Meier estimated time to DBF is 1.5 years (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 3.3 years. Median BMV is 0.4 (IQR: 0, 1.4). Distant brain failures appear to reach a plateau at four years where the cumulative incidence of DBF is 82%. Seventy percent of first time DBFs have occurred by two years. 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). <h3>Conclusion</h3> Approximately one third of brain metastasis patients who live beyond two years after initial SRS have a BMV of zero. DBFs appear to reach a plateau at four years, after which very few patients develop new brain metastases if they have not yet already. Factors significantly associated with a BMV of zero include Caucasian race and having had a single brain metastasis at first SRS.