Patient must not have leptomeningeal disease Leptomeningeal disease Leptomeningeal disease Leptomeningeal disease as the only manifestation of the current malignancy Multifocal disease or leptomeningeal disease (LM) disease on post-operative MRI; Leptomeningeal disease Leptomeningeal disease Patients with leptomeningeal disease are not eligible for participation\r\n* Please note: leptomeningeal enhancement is not an exclusion Leptomeningeal disease Known leptomeningeal disease Participants with widespread, definitive leptomeningeal disease Participants with widespread, definitive leptomeningeal disease Leptomeningeal disease Patients with leptomeningeal disease Patients with metastatic disease, including leptomeningeal or subarachnoid disseminated disease. Leptomeningeal disease Has evidence of leptomeningeal disease Patient has leptomeningeal disease Diffuse leptomeningeal gliomatosis Untreated CNS or leptomeningeal metastasis\r\n* Note: CNS or leptomeningeal disease must be stable for >= months prior to registration Patients with asymptomatic leptomeningeal disease are eligible for participation in this trial; however, patients who had progression of leptomeningeal disease on alectinib will be required to undergo CNS radiation to meet eligibility Patients with known leptomeningeal metastatic disease Patients with leptomeningeal disease Leptomeningeal disease Symptomatic or untreated leptomeningeal disease Leptomeningeal disease Patients with metastatic disease, including leptomeningeal or subarachnoid disseminated disease Has presence of diffuse leptomeningeal disease or extracranial disease Leptomeningeal disease Evidence of leptomeningeal disease Subjects with leptomeningeal disease are excluded Presence of leptomeningeal disease Diagnosis of leptomeningeal disease Evidence of leptomeningeal spread of disease Presence of leptomeningeal disease Presence of extracranial metastatic or leptomeningeal disease Leptomeningeal disease Radiographic or cytologic evidence of leptomeningeal disease Leptomeningeal disease Presence of leptomeningeal disease Presence of diffuse leptomeningeal disease Imaging or cytologic evidence of leptomeningeal disease Patients with multifocal disease or leptomeningeal disease who require whole brain radiotherapy (WBRT) Presence of leptomeningeal disease Leptomeningeal disease Patients who have leptomeningeal disease Patients with leptomeningeal disease Symptomatic or untreated leptomeningeal disease. Has infratentorial, or leptomeningeal evidence of recurrent disease Leptomeningeal disease Evidence of leptomeningeal dissemination Known leptomeningeal disease or CNS midline shifts Patients with documented evidence of leptomeningeal disease Leptomeningeal disease Leptomeningeal disease. Leptomeningeal disease Leptomeningeal disease Leptomeningeal disease Leptomeningeal disease Has infratentorial, or leptomeningeal evidence of recurrent disease Leptomeningeal disease Has presence of diffuse leptomeningeal disease or extracranial disease Leptomeningeal disease Known leptomeningeal disease Leptomeningeal disease Presence of extracranial metastatic or leptomeningeal disease Leptomeningeal disease Patients with leptomeningeal disease are excluded presence of Alzheimer's disease, meningioma, leptomeningeal disease from prostate cancer. Patients with leptomeningeal disease are not eligible for participation Patients with leptomeningeal disease Infratentorial, or leptomeningeal evidence of recurrent disease Symptomatic or untreated leptomeningeal disease Patients with leptomeningeal disease Multifocal disease or leptomeningeal spread There is radiographic evidence of leptomeningeal disease prior to study entry Patients must have CNS/ leptomeningeal disease including high risk medulloblastoma, or a CNS/leptomeningeal malignancy which is refractory to conventional therapies, or for which no conventional therapy exists, OR a recurrent brain tumors with a predilection for leptomeningeal dissemination (medulloblastoma, primitive neuroectodermal tumor [PNET], rhabdoid tumor) Evidence of leptomeningeal spread of glibolastoma or gliosarcoma. Subjects in Group are not required to have measurable disease but must have cytologic confirmation of leptomeningeal disease Leptomeningeal disease as a manifestation of cancer Leptomeningeal disease Leptomeningeal disease as a manifestation of cancer Leptomeningeal disease Symptomatic or untreated leptomeningeal disease Leptomeningeal disease Leptomeningeal disease as a manifestation of cancer Medically apparent CNS lymphoma or leptomeningeal disease Leptomeningeal disease as a manifestation of cancer Leptomeningeal disease Leptomeningeal disease as the only manifestation of the current malignancy Leptomeningeal disease Leptomeningeal disease as the only manifestation of the current malignancy Evidence of leptomeningeal spread of disease. The participant has leptomeningeal disease. Leptomeningeal disease as the only manifestation of the current malignancy Presence of diffuse leptomeningeal disease or gliomatosis cerebri. Leptomeningeal disease Leptomeningeal disease Diffuse leptomeningeal disease at recurrence Leptomeningeal disease Leptomeningeal disease Patients with primary CNS tumors and leptomeningeal disease are ineligible.