Brain irradiation is the standard of treatment for most brain tumors. Irradiating the brain prolongs patient survival, but often results in long term memory and functional impairments. These deficits are driven by radiation injury to myelinating cells, oligodendrocytes. One method to prevent deficits is to replace myelin by transplanting in new stem cells to the brain. We will test the safety and effectiveness of human glial cells to protect the brain in a model of radiation‐induced brain injury during therapy for brain cancer.