Surg-09. Efficacy of a Biweekly 3-Stage Stereotactic Radiosurgery for Large Brain Metastases: The Effect of Egfr Tyrosine-Kinase Inhibitor on Tumor Response and Clinical Outcomes

Abstract

Stereotactic radiosurgery(SRS) is one of primary treatment modalities for brain metastases(BM), however local control and radiation necrosis of large BM remain challenging. To overcome these limitations, biweekly 3-stage SRS for LBM was performed in this study. Total 53 patients were treated for 62 LBM. Female was 27(50.9%), and mean age was 63.7±11.8years. The mean KPS was 79.2±9.0 and GPA score was 1.9±0.7. Non-small cell lung cancer(NSCLC) was the most common primary cancer in 31 patients, others include 6 small cell lung cancer(SCLC), 9 gastro-intestinal tract cancer, 5 gynecological cancer, and etc. Epidermal growth factor receptor(EGFR) mutation was identified in 13 patients, and EGFR tyrosine-kinase inhibitor(TKI) was used in 10 patients during and after staged SRS. The mean tumor volume was 19.1cm3. The mean marginal dose of 11.7Gy was delivered to the 50% isodose line based on new treatment planning every two weeks. The mean tumor volume at the second and third stage was 14.8cm3 and 11.0cm3, respectively. The lesions from squamous cell carcinoma of NSCLC decreased most rapidly, and followed by gynecological cancer, SCLC and adenocarcinoma of NSCLC(volume ratio at 3rd stage was 0.39, 0.53, 0.56, and 0.64, respectively). The most significant factor related with tumor volume reduction at 3rd stage was usage of EGFR-TKI(p=0.016; LR analysis). The mean overall survival(OS) was 15.3months, and estimated OS were 62% and 46% at 6 and 12months. In the multivariate analysis, KPS(OR=0.918; 95% CI,0.871-0.968; p=0.002) and usage of EGFR-TKI(OR=0.216; 95% CI,0.059-0.790; p=0.021) were significantly associated with OS. The mean OS of the group of usage of EGFR-TKI was significantly longer than that of the others(20.7months, and 13.1months; p=0.029; log-rank test). The biweekly 3-stage SRS seems to be effective treatment for patients with LBM, especially in patients who were treated with EGFR-TKI during and/or after SRS, also cautiously considering the primary tumor origin.