Study of Proton Radiation to the Brain and Spinal Cord for Patients With Leptomeningeal Metastases

Inclusion Criteria:

* Female subjects must either be of non-reproductive potential (i.e. post-menopausal by history: \>/= 60 years old and 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 with solid tumor malignancy with leptomeningeal metastases established radiographically and/or through CSF cytology.
* KPS ≥ 60.
* Age ≥ 10 years.
* For adult patient, the patient is able to provide informed consent. For pediatric patient, a parent is able to provide informed consent.
* Patient at reproductive potential must agree to practice an effective contraceptive method.
* Adequate bone marrow function:

  * Hemoglobin ≥ 8g/dL
  * Absolute neutrophil count ≥500/mm\^3
  * Platelet count ≥ 100,000/mm\^3

Exclusion Criteria:

* Patient with multiple, serious major neurologic deficits 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.