RADT-14. EARLY OUTCOMES FROM PROTON CRANIOSPINAL IRRADIATION FOR LEPTOMENINGEAL METASTASIS FROM SOLID TUMORS

Abstract INTRODUCTION Treatment options for leptomeningeal metastasis (LM) are limited. A phase II study found that proton craniospinal irradiation (pCSI) was well-tolerated and improved survival. We report our experience with pCSI for solid-tumor LM. METHODS This is a retrospective review of patients treated with pCSI for solid-tumor LM from December 2020 to January 2024 at our center. Patient characteristics were summarized using descriptive statistics. Median overall survival (OS) and median central nervous system progression-free survival (CNS-PFS) from the first day of pCSI were estimated using Kaplan-Meier survival curves. RESULTS We identified 45 patients who completed pCSI. Median age was 54 years (range, 23-79); 73% were female, and 53% lived more than 100 miles from our center. Breast cancer (53%), lung cancer (20%), and melanoma (9%) were the most common primary cancers; 51% of patients had stable systemic disease at LM diagnosis. All had imaging evidence of LM, and 64% were confirmed by cytologic examination of the cerebrospinal fluid. Eighty percent had symptomatic LM, and the median Karnofsky Performance Scale (KPS) at LM diagnosis was 80. The median time from primary cancer diagnosis to LM diagnosis was 23.1 months (range, 0-221.3). Fifty-three percent of patients had active brain metastasis at LM diagnosis. At the first visit following pCSI, median KPS was 70. Seventy-six percent reported new or worsening nausea, 51% headache, and 31% fatigue. Following pCSI, 18% received LM surveillance, 4% intrathecal chemotherapy, 67% systemic therapy, 9% hospice care, and 2% lost to follow-up. Median OS was 13.7 months (95% confidence interval [CI], 11.2 to infinity), and median CNS-PFS was 6.5 months (95% CI, 4.9 to 12.8). CONCLUSIONS The outcomes in our cohort are comparable to those recently reported in a phase II trial. Further study is indicated to determine the optimal candidates for pCSI and sequential therapies.