This study is to compare the usual treatment (radiation plus temozolomide alone) to using the study treatment (usual treatment plus the study drug, vorasidenib). The addition of the study drug, vorasidenib, to the usual treatment could shrink or stabilize your cancer. The study drug is FDA (Food and Drug Administration approved. The study drug will be given orally. The study will randomize (the computer will pick the group that the participant will be enrolled in) participant to Group 1 or Group 2. Participants can expect to be on the trial for 10 years or more. There will 4 participants enrolled locally.