RATIONALE: Radiation therapy uses high-energy x-rays to kill tumor cells. Giving radiation therapy in higher doses over a shorter period of time may kill more tumor cells and have fewer side effects. 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. It is not yet known whether standard radiation therapy, higher-dose radiation therapy, or chemotherapy is more effective in treating older patients with glioblastoma multiforme.