Specific aims for this project include: 1. Determine if glutamate can be measured quantitatively in intrapatient as well as interpatient settings. 2. Determine if external beam radiotherapy affects glutamate metabolism. 3. Determine if external beam radiotherapy preferentially affects glutamate metabolism in the various substructures in the brain. 4. Do changes in glutamate signals correlate to neurocognitive changes? We will be able to compare the glutamate metabolism data acquired form imaging to serum marker data being collected from NIH Protocol 08-C-0214 - A pilot study to measure neurocognitive changes from whole brain radiotherapy. A pilot study to address these aims, Validation of Glutamate-CEST Imaging in the Brain, is currently pending approval by the IRB.