This phase I trial tests the safety, side effects, and best dose of triapine in combination with radiation therapy in treating patients with glioblastoma or astrocytoma that has come back after a period of improvement (recurrent). Triapine may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Radiation therapy uses high energy x-rays, particles, or radioactive seeds to kill cancer cells and shrink tumors. Giving triapine in combination with radiation therapy may be safe, tolerable, and/or effective in treating patients with recurrent glioblastoma or astrocytoma.