P11.31.B LEPTOMENINGEAL SPREAD AFTER POSTOPERATIVE STEREOTACTIC RADIOTHERAPY FOR BRAIN METASTASES

Abstract BACKGROUND Stereotactic radiotherapy (SRT) is the preferred treatment after surgical resection of brain metastases to improve local tumour control compared to observation. Some recent studies suggest that leptomeningeal metastases (LMM) occur more often after postoperative SRT compared to primary SRT with brain metastases in situ. This may be caused by tumour cells spillage during surgery. The aim of this study was to determine the incidence of LMM after postoperative SRT of brain metastases in our institution. MATERIAL AND METHODS All patients treated with postoperative SRT for brain metastases in our hospital between 2015 and 2020 were included in this retrospective analysis. LMM was diagnosed by a neuro-radiologist (RH) on a cerebral MRI. LMM, overall survival, and time to local recurrence (LR) were estimated from date of SRT, using the Kaplan-Meier method. RESULTS In total, 53 patients with 84 brain metastases were included in the analysis. Median age at SRT was 58 years (range 45 - 75 years). Median survival in this cohort was 16 months (IQR 9 - 26 months). Eight of 53 patients (15%) developed LMM at a median of 9 months after SRT. Using Kaplan-Meyer analysis, the incidence of LMM at 1 and 2 years was 15% and 19%, respectively. Twelve patients (23%) of 53 experienced LR at a median of 9 months. The 1 and 2-year actuarial incidence was 14% and 35%, respectively. CONCLUSION In our cohort, the incidence of LMM after postoperative SRT for brain metastases is comparable to other studies. Studies are needed to determine whether the incidence of LMM after postoperative SRT can be reduced.