Capecitabine is an oral chemotherapy that is given to patients with other types of cancer. The study will evaluate whether the dosage of 1500 mg/m2 of capecitabine is tolerable after radiation, when taken along with temozolomide. It will also try to determine if the medication capecitabine helps patients respond to treatment for a longer period of time compared to just temozolomide alone, which is the standard of care.