New radiation approach targets cancer in the brain and spine

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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) Exclusion Criteria: * Chemotherapy, biological therapy, immunotherapy within 7 days prior to day 1 of protocol therapy * Any prior radiation that in the opinion of the investigator unable to respect normal tissue tolerances and preclude craniospinal irradiation * Patients with multiple or serious major neurologic symptoms (including encephalopathy) per physician / investigator assessment * Patients with extensive, uncontrolled extracranial systemic disease * Patients without reasonable systemic treatment options per physician / investigator * Other clinically significant uncontrolled illness per opinion of physician / investigator * Patients with a history or evidence of HIV infection (unless on effective anti-retroviral therapy with undetectable viral load based on prior tests within 6 months are eligible for this trial) * Patients with history or evidence of chronic hepatitis B virus (HBV) infection (unless HBV viral load is undetectable based on prior tests and on suppressive therapy) * Patients with a history or evidence of hepatitis C virus (HCV) infection unless treated and cured. (Patients with HCV infection who are currently on treatment are eligible if they have an undetectable HCV viral load based on prior tests) * 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)