RADT-05. CLINICAL OUTCOMES OF PROTON CRANIOSPINAL IRRADIATION FOR PATIENTS WITH LEPTOMENINGEAL CARCINOMATOSIS

Abstract

Abstract Leptomeningeal carcinomatosis (LC) is a devastating complication of metastatic tumors. Radiotherapy (RT) is integral to LC treatment, and proton craniospinal irradiation (CSI) may make RT more effective by targeting the entire central nervous system (CNS) compartment. We evaluated outcomes in patients treated with proton CSI for LC. We identified 56 patients treated with proton CSI for LC between 2018 and 2020 at our institution. Data on patient demographics, disease and treatment history, cerebrospinal fluid circulating tumor cells (CSF CTCs), and gene alterations were collected. Kaplan Meier analysis and Cox regression models were used to compare correlates with CNS time to progression (TTP), CNS progression-free survival (PFS) and overall survival (OS). Most patients had non-small cell lung cancer (NSCLC, n=27, 48%) or breast cancer (n=21, 38%). The median age was 58 (30-77), and median KPS was 80 (60-90). The median RT dose was 30Gy (25-36). The median follow-up was 12 months (1-22), with 26 (46%) patients alive at the last follow-up. Of 35 (63%) patients who progressed, 6 (11%) progressed in the CNS, 13 (23%) progressed systemically, and 16 (29%) progressed in both. The median TTP, PFS and OS was 8 months (1-21), 6 months (1-21) and 8 months (1-22), respectively. No difference in PFS (7 vs. 6 months, p=0.6) and OS (8 vs. 7 months, p=0.3) was observed between patients with NSCLC and breast cancer. Of patients alive at 3 months, 79% showed stable or improved functional status after CSI. Decreased CSF CTCs immediately post CSI had significantly improved PFS (8 vs. 5 months with no CTC decrease, HR=0.3, p=0.02). Lastly, we identified genetic correlates with survival outcomes. Proton CSI appears to be a promising treatment for LC in select patients, resulting in prolonged CNS disease control and survival. A randomized trial is currently underway to assess its efficacy prospectively.