Inclusion Criteria:  Cohort A: histological diagnosis of IDH-mutant astrocytoma or oligodendroglioma, WHO grade II-IV. IDH-mutation may be either by immunohistochemistry (IHC) or next-generation sequencing (NGS) as per routine clinical care. Cohort B: histological diagnosis of IDH-wildtype astrocytoma, WHO grade II-IV. IDH-wildtype status or absence of IDH-mutation may be either by IHC or NGS as per routine clinical care. The IDH-wildtype patients should have >80% probability to be alive in 6 months, and the online nomogram calculator below may be used to estimate the 6-month probability: http://cancer4.case.edu/rCalculator/rCalculator.html (Gittleman et al., 2016). Cohort C: any non-infiltrative benign brain tumor histology, including but not limited to meningioma, pituitary tumor, schwannoma, craniopharngioma, hemangioblastoma, hemangiopericytoma, pineal tumor, pilocytic astrocytoma, and ganglioglioma. The tumor should be in the supratentorium, excluding brainstem and cerebellum. At least 18 years of age. Karnofsky performance status (KPS) of at least 70% Eligible for and planning to receive standard fractionated RT, which can be either photon-based or proton beam therapy. May be part of other clinical trials and can receive chemotherapy or experimental agents concurrently with or after RT as long as the other clinical trial does not exclude participation in this non-therapeutic study. Females of childbearing potential (defined as a female who is non-menopausal or surgically sterilized) must be willing to use an acceptable method of birth control (i.e., hormonal contraceptive, intra-uterine device, diaphragm with spermicide, condom with spermicide, or abstinence) for the duration of the study. Should a woman become pregnant or suspect she is pregnant while participating in this study, she must inform her treating physician immediately. Able to understand and willing to sign an IRB-approved written informed consent document (legally authorized representative permitted).  Exclusion Criteria:  Prior cranial RT or RT to the head and neck where potential field overlap may exist Gliomatosis, leptomeningeal, or metastatic involvement. Medical contraindication to MRI (e.g., unsafe foreign metallic implants, incompatible pacemaker, inability to lie still for long periods, severe to end-stage kidney disease or on hemodialysis). Require anesthesia to undergo MRI (e.g. severe claustrophobia), which would interfere with RS-fMRI acquisition and processing. Pregnant or breastfeeding. Non-English speaking, as the cognitive assessments will only be available in English.