RADI-07. GAMMA KNIFE RADIOSURGERY FOR SMALL CELL LUNG CANCER: PROGNOSTIC FACTORS INCLUDING ADDITIONAL LESIONS IDENTIFIED ON THE DAY OF RADIOSURGERY

OBJECTIVES: Prophylactic cranial irradiation (PCI) and whole brain radiation (WBRT) are standard of care for intracranial disease in small cell lung cancer (SCLC) patients. We sought to identify predictors of overall survival (OS) in SCLC patients treated with salvage Gamma Knife radiosurgery (GKRS) for brain metastases after prior WBRT or PCI. METHODS: Retrospective analyses were conducted on 26 SCLC patients treated with GKRS at one institution between May 2010 and June 2018. Factors predictive of OS were analyzed using Cox proportional hazards regression and Wilcoxon sum-rank testing. RESULTS: Median follow-up and median OS following GKRS was 6.6 mos (range 0.7–24.2 mos). Median OS was 21.4 mos from initial diagnosis (range 7.3–49.3 mos). Presence of extracranial metastases at the time of GKRS was not significantly associated with median OS after GKRS (5.8 mos for patients with extracranial metastases vs 7.2 mos for patients without, p=0.425). Mean number of lesions was 2.7 (range 1–10) on diagnostic brain MRIs and 4.1 (range 1–12) on GKRS planning MRIs. Eleven patients (42%) had the same number of lesions between diagnostic MRI and GKRS MRI, and 15 patients (58%) had additional lesions on the GKRS MRI. Number of lesions treated and total tumor volume were not associated with median OS. Patients who had additional lesions on GKRS MRI compared to diagnostic MRI had lower median OS from initial diagnosis of SCLC (29.9 mos vs 18.1 mos, p=0.0182) and a trend toward lower median OS from time of GKRS (7.3 mos vs 4.8 mos, p=0.0547) compared to patients who did not have additional lesions. CONCLUSIONS: Finding additional brain metastases on GKRS planning MRIs is associated with decreased OS in SCLC patients treated with salvage GKRS. Presence of extracranial metastases at the time of GKRS and number or total volume of brain metastases were not associated with OS.