Proton Cranio-spinal Irradiation for Leptomeningeal Metastasis

Inclusion Criteria: * Metastasis to the leptomeningeal space (LM) surrounding the brain and/ or spinal cord * Metastasis verified by MRI or CSF cytology * Karnofsky \>=60 (requiring some help, can take care of most personal requirements) * Adequate bone marrow function * Haemoglobin \> 5 mmol/l * Absolute neutrophil count \>1 10\^9/l * Platelet count \> 100 10\^9/l * Patient consent * Female subjects must either be of non-reproductive potential ( ≥ 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 pregnancy test within 2 weeks prior to starting treatment. * Patient at reproductive potential must agree to practice an effective contraceptive method. Exclusion Criteria: * • Previous radiotherapy to the intended treatment site that precludes developing a treatment plan that respects normal tissue tolerances (Yang) * 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 * Pregnant or lactating women.