RADI-28. UP-FRONT SINGLE SESSION RADIOSURGERY FOR LARGE BRAIN METASTASES - VOLUMETRIC RESPONSES AND OUTCOMES

OBJECTIVE: Patients presenting with large brain metastases (LBM), described in the literature as ≥2.5 cm in maximum diameter or ≥10cm(3)in volume, pose a management challenge. For patients not compromised by mass effect, corticosteroid therapy followed by SRS allows for efficient, minimal access care that facilitates immediate institution of systemic therapy. METHODS: We performed a volumetric-based analysis in order to determine the efficacy of single-session SRS in the treatment of LBM in comparison to other treatment modalities. Thirty patients over the age of 18 with systemic cancer and brain metastases (≥2.7cm in greatest diameter or ≥10cm(3)in volume) who underwent single session SRS were included. Serial tumor volumes, clinical outcomes, and medication requirements were studied. RESULTS: Among 30 patients, 70% of patients had either lung, melanoma, or breast cancer. Median initial tumor size (maximum diameter) was 32mm (range 28–43) and median initial tumor volume was 9.32cm(3) (range 1.09–25.31). Median marginal dose was 16Gy (range 12–18). Average percent decrease in tumor volume was 50% on imaging at 4–8 weeks, 60% at 4–6 months, 48% at 6–8 months, and 67% at >8 months compared to initial imaging. Only one patient required a subsequent craniotomy 4 years after SRS for an enlarging cyst which was granulation tissue consistent with radiation effects on pathology. There were no adverse events immediately following SRS. Median corticosteroid use after SRS was 21 days. There was no statistically significant difference in KPS score between treatment day and last follow up, suggesting relative safety and maintenance of function. CONCLUSION: Initial high dose corticosteroid therapy followed by prompt single session SRS is a safe and efficacious method of managing patients with large brain metastases (defined in our study as ≥2.7cm or ≥10cm(3)), if the clinical condition of the patient is acceptable at presentation.