Temozolomide and Radiation Therapy in Treating Patients With Newly Diagnosed Glioblastoma Multiforme or Anaplastic Astrocytoma

RATIONALE: Drugs used in chemotherapy, such as temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Radiation therapy uses high-energy x-rays to kill tumor cells. Specialized radiation therapy that delivers a high dose of radiation directly to the tumor may kill more tumor cells and cause less damage to normal tissue. Giving chemotherapy together with radiation therapy may kill more tumor cells. PURPOSE: This phase I trial is studying the side effects and best dose of temozolomide when given together with radiation therapy in treating patients with newly diagnosed glioblastoma multiforme or anaplastic astrocytoma.