Metabolic Tumor Volumes in Radiation Treatment of Primary Brain Tumors

* Metabolic Tumor Volume (MTV), identified by Magnetic Resonance Spectroscopic Imaging (MRSI) is different from the Clinical Target Volume (CTV) used for radiation dose delivery in the treatment of brain tumors. * If MTV \> CTV, the investigators hypothesize that the difference in volumes (cc) is related to worse clinical outcome. Furthermore, in case of local recurrence, the lesion is located in the MTV area that is outside of the CTV. * Alternatively, if CTV \> MTV, then the difference in volumes is related to higher treatment toxicity.