Hypofractionated Stereotactic Irradiation (HFSRT) With Pembrolizumab and Bevacizumab for Recurrent High Grade Gliomas

Radiation therapy treatment (FSRT) which will be given to participants over 5 days.

"Dose Escalation: The dose of pembrolizumab will be escalated per schema in a 3+3 fashion. The starting dose (i.e., dose level 1) will be 100 mg.~Dose Expansion: The pembrolizumab dose used in the dose expansion cohort will be maximum tolerated dose (MTD) determined from the dose escalation phase."

Initial cycle of bevacizumab must start within 10 days of registering to the trial. It will be given concurrent with radiation therapy. Bevacizumab will be administered intravenously at a dose of 10 mg/kg every 2 weeks. Doses will be adjusted if there is a \> 10% change in weight.