<qa>  What is gefitinib used to stop growth of tumor cells?This phase III trial studies the side effects and best dose of gefitinib when given together with radiation therapy and to see how well it works in treating patients with glioblastoma multiforme. Gefitinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high energy x rays to kill tumor cells. Giving gefitinib together with radiation therapy may be an effective treatment for glioblastoma multiforme. 