This study will collect blood and urine samples from patients undergoing radiation therapy for glioblastoma multiforme (a type of brain tumor) to investigate the effects of this treatment on blood cells and certain proteins. The information from this study may help scientists develop new tests to measure radiation exposure and find new ways to treat cancer with radiation, and help determine which kinds of patients or tumors respond better to radiation therapy. Two proteins of particular interest in this study and which may be involved in the recurrence of cancer are VEGF (vascular endothelial growth factor) and MMPs (matrix metalloproteinases). Patients 18 years of age and older with glioblastoma multiforme who are receiving or will receive radiation therapy as part of their medical treatment may be eligible for this study. Candidates are screened with a history and physical examination, blood tests, and magnetic resonance imaging (MRI) of the brain. Participants will have blood and urine samples collected before, during and after completion of their radiation treatment. Urine samples are collected in a cup and about 2 tablespoons of blood are withdrawn through a needle in a vein. Additional samples may be requested at different times during treatment and in the 3-year follow-up period.