The goal of this trial is to determine whether it is possible to minimize radiation dose to parts of the brain that are important for thinking and learning in children who require radiation to treat their tumor, and if this will help reduce neurocognitive (thinking and learning) impairments in these patients. Patients with newly diagnosed brain or head and neck tumors who are having radiation therapy will have neurocognitive testing and MRI imaging (both research and for regular care) done as part of their participation in the study. Survivors of childhood brain tumors who completed radiation therapy at least two years before joining the study, and have not had a recurrence, will have neurocognitive testing and research MRIs completed. Healthy children will also be enrolled and have research MRIs done. The researchers will use the radiation plan to determine how much radiation was delivered to different parts of the brain. The investigators will use the MRIs to determine how the normal brain is changing after treatment; and how this compares to patients who had standard radiation treatment or who never had a brain tumor. The neurocognitive testing will be compared among different groups to see how different treatment plans affect performance on neurocognitive tests.