RADT-08. ADJUVANT SBRT FOR RESECTED BRAIN METASTASES: THE EFFECT OF TIMING ON LONG-TERM INTENDED-FIELD CONTROL
Abstract INTRODUCTION Adjuvant stereotactic body radiation therapy (SBRT) improves the local control of resected brain metastases (BrM). However, the dependency of long-term outcomes on SBRT timing relative to surgery remains unclear. METHODS Retrospective analysis of metastasectomy-plus-adjuvant-SBRT patients at Memorial Sloan Kettering (MSK) between 2013-2016 was conducted. Kaplan-Meier methodology was used to describe overall survival (OS) and cumulative incidence in a competing-risks setting recurrence at the surgical site, other SBRT-treated sites, and elsewhere in the brain as defined by RANO-BM criteria. Recursive partitioning analysis (RPA) and competing-risks regression modeling assessed prognostic variables and associated events of interest. RESULTS Two hundred eighty-two patients with BrM including non-small cell lung (34%), breast (16%), melanoma (13%), and other cancers were included. Median time-to-adjuvant-SBRT (TT-SBRT) was 34 days (IQR: 27-39). Median overall survival (OS) from SBRT was 1.5 years (95% CI: 1.2-2.1) with median follow-up of 49.8 months for survivors. Local surgical recurrence, other irradiated-site, and distant progression rates were 14.3% (95%CI: 10.1-18.5), 4.9% (95%CI: 2.3-7.5), and 47.5% (95%CI: 41.4-53.6) at 5 years, respectively. TT-SBRT as a continuous variable significantly associated with surgical-site recurrence (HR 1.05 [1.02-1.07], p=0.0003), but not with distant or other irradiated-site recurrence nor OS. RPA analysis demonstrated the greatest control rate advantage with TT-SBRT < 39 days (HR for 39+ days: 2.81 [1.50-5.27], p=0.001). No association of TT-SBRT with radiation necrosis, wound complication, or development of leptomeningeal dissemination was identified. CONCLUSIONS Delays in initiation of post-operative SBRT can decrease its efficacy. Efforts must be made to minimize logistical, procedural, and socioeconomic factors responsible for these delays.