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

Inclusion Criteria

• •Documented informed consent of the participant and/or legally authorized representative
• •* Assent, when appropriate, will be obtained per institutional guidelines
• •≥ 18 years
• •Karnofsky performance status (KPS) ≥ 60
• •Ability to read and understand English or Spanish for questionnaires, or ability to complete questionnaires using certified interpreter
• •Histologically confirmed breast cancer or non-small cell lung cancer
• •Leptomeningeal disease established either radiographically and/or CSF cytology
• •Absolute neutrophil count (ANC) ≥ 1,000/mm\^3
• •Hemoglobin ≥ 8 g/dL
• •Platelet ≥ 100,000/mm\^3
• •Creatinine clearance of ≥ 50 mL/min per 24 hour urine test or the Cockcroft-Gault formula
• •Women of childbearing potential (WOCBP): negative urine or serum pregnancy test
• •* If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required
• •Agreement by females and males of childbearing potential to use an effective method of birth control or abstain from heterosexual activity for the course of the study through at least 1 month after the last dose of protocol therapy
• •* Childbearing potential defined as not being surgically sterilized (men and women) or have not been free from menses for \> 1 year (women only)
• •Other active malignancy. Patients with a prior or concurrent malignancy whose natural history or treatment does not have the potential to interfere with the safety or efficacy assessment of the study are eligible for this trial
• •Females only: Pregnant or breastfeeding
• •Any other condition that would, in the investigator's judgment, contraindicate the patient's participation in the clinical study due to safety concerns with clinical study procedures
• •Unable to undergo MRI brain and spine with gadolinium contrast
• •Prospective participants who, in the opinion of the investigator, may not be able to comply with all study procedures (including compliance issues related to feasibility/logistics)