Radt-06. Volume Kinetics Following Two-Session Gamma Knife Radiosurgery for Large Brain Metastases (Bm)

Abstract

INTRODUCTION Resection is a well-established treatment for BM ≥ 2 cm, albeit with potential for perioperative complications and delays in systemic treatment. Staged stereotactic radiosurgery (S-SRS) may improve outcomes versus traditional SRS, representing an alternative to surgery in responders. We reviewed institutional outcomes using 2-session S-SRS, focusing on lesion volume kinetics. METHODS 25 patients with 27 lesions underwent S-SRS at our institution between 2014 and 2020. Tumor volumes (TV) were measured at both S-SRS sessions and on follow-up MRI studies. RESULTS Median age at S-SRS was 61 years (range (r:) 31–84). Nine patients (10 BM) were lost to follow-up. Two patients failed to receive their second S-SRS due to local progression. The median margin tumor doses at first and second S-SRS were 15 Gy (r: 12–18 Gy) and 15 Gy (r: 12–16 Gy). The median interval between stages was 32 days (r: 8–63), and median TV at the first and second stages were 9.3 cm3 (r: 1.5–34.7 cm3) and 3.3 cm3 (r: 0.76–26.1 cm3), respectively. The median absolute and relative decrement between S-SRS sessions was 3.7 cm3 (r: 2.8-16.5 cm3) and 49.5% (r: 17.1-87.1%), respectively. [1-2]-month, [3-5]-month, and [6-12]-month MRI scans were available for 17, 10, and 15 lesions. The median decrease in TV compared to baseline was 50.2%, 78.2%, 74.9%. Two of 17 lesions (12%) had initial control but subsequently experienced volumetric progression and required resection. There were no G3+ adverse events (AE). Crude tumor control was achieved in 14 of 17 individual lesions (82%). CONCLUSION Two-session S-SRS is an effective treatment modality for treating patients with large BM, which is feasible in over 80% of patients with sustained tumor control and early volumetric regression.