RADI-05. Metastatic Neoplasm Volume Kinetics Following Two-Staged Stereotactic Radiosurgery

INTRODUCTION: Multisession staged stereotactic radiosurgery (2-SSRS) represents an alternative approach for management of large brain metastases (LBMs), with potential theoretical advantages over fractionated SRS and represents an alternative to surgery in poor surgical candidates. We aimed to investigate the clinical efficacy and safety of 2-SSRS in patients with LBMs. METHODS: LBMs of patients treated with 2-SSRS between 2014 and 2020 were evaluated. Demographic, clinical, and radiologic information was obtained. Volumetric measurements at first SSRS, second SSRS, and follow-up imaging studies were obtained. RESULTS: Twenty-six patients with 28 LBMs were included in the study. Fifteen patients (58%) were male. Median age at 2-SSRS was 61 years (range: 31–84). Median marginal doses for first and second SSRS were 15 Gy (range: 12–18 Gy) and 15 Gy (range: 12–16 Gy), respectively. Median duration between sessions was 32 days. Two patients (8%) failed to receive their second SSRS due to local progression. Median tumor volumes at first SSRS, second SSRS, 3-month follow-up, and 6-month follow-up were 8.7 cm3 (range: 1.5–34.7 cm3), 3.3 cm3 (range: 0.8–26.1 cm3), 1.7 cm3 (range: 0.2–10.1 cm3), and 1.4 cm3 (range: .04–20.7 cm3), respectively. The median absolute and relative decrement between S-SRS sessions was 3.7 cm3 (range: 2.8–16.5 cm3) and 49.5% (range: 17.1- 87.1%), respectively. Overall, 26 of the 28 lesions (93%) demonstrated early local control following the first SSRS with 18 lesions (69%) demonstrating a decrease in volume of >30% and 3 lesions (12%) remaining stable. Six lesions (23%) showed disease progression. There were no grade 3 adverse events. CONCLUSIONS: Our study supports the effectiveness and safety of 2-SSRS as a treatment modality for patients with large, symptomatic brain metastases, especially in non-surgical candidates. The local failure rate and low occurrence of adverse effects are comparable to other staged radiosurgery series.