This phase III trial compares the effectiveness of fractionated stereotactic radiosurgery (FSRS) to usual care stereotactic radiosurgery (SRS) in treating patients with cancer that has spread from where it first started to the brain. Radiation therapy uses high energy x-rays to kill tumor cells and shrink tumors. FSRS delivers a high dose of radiation to the tumor over 3 treatments. SRS is a type of external radiation therapy that uses special equipment to position the patient and precisely give a single large dose of radiation to a tumor. FSRS may be more effective compared to SRS in treating patients with cancer that has spread to the brain.

The purpose of the study is to evaluate the safety and survival of carmustine wafers and radiation and retifanlimab with or without temozolomide (TMZ) in newly-diagnosed adult subjects with glioblastoma multiform after carmustine wafer placement.