RecruitingDiagnostic testDeveloping a New MRI Technique to Understand Changes in Brain Tumors After TreatmentThe purpose of this study is to develop and test a new magnetic resonance imaging (MRI) technique to see if it can be used to tell the difference between tumor growth from worsening of cancer and growth from the effects of treatment in participants who have brain tumors treated with radiation therapy called stereotactic radiosurgery (SRS).