RecruitingRadiation therapyPrOton Pulsed reduCed dOse Rate Radiotherapy for Recurrent CNS maligNancies TrialThe purpose of this research study is to see if a specific type of radiation therapy, called "proton pulsed reduced dose rate" or "PRDR radiotherapy" has any benefits at dose levels and number of fractions thought to be acceptable in earlier research studies. The researchers want to find out what effects (good and bad) PRDR has on people with cancer in the brain called a "recurrent high-grade glioma" meaning that it grows fast, can spread quickly, and it has come back or gotten worse after being treated previously.