 Radiation therapy uses high-energy x-rays to kill tumor cells. Drugs used in chemotherapy, such as etoposide, carboplatin and cisplatin, 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 which radiation therapy regimen is more effective when given together with chemotherapy in treating patients with limited-stage small cell lung cancer. This randomized phase III trial is comparing different chest radiation therapy regimens to see how well they work in treating patients with limited-stage small cell lung cancer. 