RecruitingProcedureMRI in High-Grade Glioma Patients Undergoing ChemoradiationThe purpose of this research study is to see if investigators can predict how brain functioning changes after radiation treatment based on PET scans and blood tests. Most participants experience at least mild decreases in their memory or attention after radiation therapy. Investigators hope that PET scans, lumbar puncture, and blood tests might help investigators predict who might have larger changes in their brain function after radiation.