Photon Craniospinal Irradiation for the Treatment of Leptomeningeal Disease Secondary to Breast Cancer or Non-small Cell Lung Cancer

PRIMARY OBJECTIVE: I. To evaluate the efficacy of photon-VMAT-CSI; assessed by median central nervous system progression free survival (CNS-PFS). SECONDARY OBJECTIVES: I. To estimate and assess central nervous system (CNS) response rate, response duration, and overall survival probability. II. To summarize and assess toxicities including: type, frequency, severity, attribution, time course and duration. III. To characterize and evaluate patient reported outcomes (PROs), including quality of life (QOL), measures: IIIa. QOL Questionnaire Brain 20 (European Organization for Research and Treatment of Cancer \[EORTC\]-Quality of Life Questionnaire \[QLQ\]-Brain 20 \[BN20\]); IIIb. Core QOL Questionnaire 30 (EORTC-QLQ-Core 30 \[C30\]); IIIc. Patient reported outcomes measurement information system (PROMIS) for Anxiety; IIId. PROMIS Cognition. EXPLORATORY OBJECTIVES: I. To characterize inflammatory markers over time. II. To explore the potential association between inflammatory markers and radiation-related toxicity. III. To evaluate the potential association between circulating cell-free deoxyribonucleic acid (cfDNA), imaging, and response. IV. To evaluate possible genomic predictors of CNS progression. OUTLINE: Patients undergo photon-VMAT-CSI once daily (QD) for 10 treatments over 10-20 days (Monday-Friday) in the absence of disease progression or unacceptable toxicity. Patients undergo magnetic resonance imaging (MRI) during screening and follow-up and undergo collection of blood samples throughout the trial. Patients also undergo lumbar puncture LP or Ommaya reservoir tap for cerebrospinal fluid (CSF) sample collection during screening and follow-up. After completion of study treatment, patients are followed up at 1 month and then every 3 months for up to 1 year.