IDH3A and primary central nervous system lymphoma: CNS: central nervous system; IDH: isocitrate dehydrogenase; IMRT: intensity-modulated radiation therapy; MRS: magnetic resonance spectroscopy; MRP: magnetic resonance perfusion; PCNSL: primary central nervous system lymphoma; RT: radiation therapy; SRS: stereotactic radiosurgery; WBRT: whole brain radiation therapy