The investigators are doing this study to find out whether proton craniospinal radiation therapy (proton CSI) or partial photon radiation therapy is more effective at preventing leptomeningeal metastasis from worsening. The proton CSI targets the entire space containing the CSF, brain, and spinal fluid. The partial photon radiation therapy treats only areas where the patient is having symptoms, such as the entire brain or part of the spine. The investigators also want to find out if proton CSI improves the symptoms patients may be experiencing because of the leptomeningeal metastasis. In addition, the investigators will compare the side effects of proton CSI and partial photon therapy.

Patients undergoing proton beam RT will receive their treatment at the New York Proton Center in New York, NY. As part of the New York Proton Consortium, MSK has contracted for its faculty to treat patients at the New York Proton Center. If it is unfeasible for patients to get treated at NYPC, patients will have the decision to get treated at ProCure in Summerset, NJ.

Inclusion Criteria:

• Patient with solid tumor malignancy with leptomeningeal metastases established radiographically and/or through CSF cytology

• Patients who are candidates for radiation therapy for the treatment of leptomeningeal metastases

• Patients of all ages

• KPS ≥ 60 for participants ≥ 16 years old, and Lansky ≥ 60 for participants < 16 years old

• For adult patient, the patient/ legally authorized representative is able to provide informed consent. For pediatric patient, a parent is able to provide informed consent.

• Adequate bone marrow function:

  • Hemoglobin > 8g/dL
  • Absolute neutrophil count >1,000/mm
  • Platelet count > 100,000/mm

• Female subjects must either be of non-reproductive potential (i.e. pediatric patients, OR postmenopausal by history [≥ 60 years old, or with no menses for >1 year without an alternative medical cause], OR history of hysterectomy, OR history of bilateral tubal ligation, OR history of bilateral oophorectomy) or must have a negative serum pregnancy test within 2 weeks prior to starting treatment.

• Patient at reproductive potential must agree to practice an effective contraceptive method.

Exclusion Criteria:

• Patient with multiple, serious major neurologic deficits per physician/investigator assessment including encephalopathy
• Patient with extensive systemic disease and without reasonable systemic treatment options
• Patient who is unable to undergo MRI brain and spine with gadolinium contrast
• Previous radiotherapy to the intended treatment site that precludes developing a treatment plan that respects normal tissue tolerances
• Pregnant or lactating women.

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.