RATIONALE: Radiation therapy uses high-energy x-rays to kill tumor cells. Drugs used in chemotherapy, such as arsenic trioxide and temozolomide, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Arsenic trioxide and temozolomide may also make tumor cells more sensitive to radiation therapy. Giving radiation therapy together with combination chemotherapy may kill more tumor cells.