Additional Study Information: Phase 2, Treatment A: This study is being done to see if your recurrent brain tumor may respond to a combination of radiosurgery (a type of radiation therapy) with nivolumab (a type of immunotherapy drug). A small number of patients have already received this combination previously and have tolerated the treatment relatively well. However, we would like to see if the combination treatment may be better or worse than the standard approach of radiosurgery alone. We would also want to learn more about the side effects associated with giving nivolumab with radiosurgery. Phase 2, Treatment B: This study is being done to see if your recurrent brain tumor may respond to a combination of radiosurgery (a type of radiation therapy) with nivolumab and ipilimumab (two types of immunotherapy drugs). A small number of patients have already received this combination previously and have tolerated the treatment relatively well. However, we would like to see if the combination treatment may be better or worse than the standard approach of radiosurgery alone. We would also want to learn more about the side effects associated with giving nivolumab and ipilimumab with radiosurgery. We are doing this study because there is currently a lack of effective methods to treat this type of brain tumor that has returned after prior radiation therapy. We want to find out if this approach is better or worse than the usual approaches that most people get for your type of brain tumor.