PURPOSE: To prospectively evaluate the feasibility of delivering 70 Gy once-daily thoracic radiotherapy (TRT), concurrent with chemotherapy, in the treatment of limited-stage small-cell lung cancer (L-SCLC). MATERIALS AND METHODS: Eligible patients received two cycles of induction paclitaxel (175 mg/m(2) on Day 1) and topotecan (1 mg/m(2) on Days 1-5) with granulocyte colony stimulating factor support, followed by three cycles of carboplatin (area under the curve = 5 on Day 1) and etoposide (100 mg/m(2) on Days 1-3). TRT (70 Gy, 2 Gy/fx/7 weeks) was initiated with the first cycle of carboplatin and etoposide. Prophylactic cranial irradiation was offered to patients achieving a complete response or good partial response. RESULTS: Ninety percent of patients (57 of 63) proceeded to protocol TRT. There was one treatment-related fatality. Nonhematologic Grade 3/4 toxicities affecting more than 10% of patients, during or after TRT, were dysphagia (16%/5%) and febrile neutropenia (12%/4%). The response rate to all therapy was 92% and the median overall survival is 22.4 months (95% confidence interval 16.1, infinity ). Twenty-eight patients remain alive with a median follow-up of 24.7 months. CONCLUSION: 70 Gy once-daily TRT can be delivered safely in the cooperative group setting for patients with L-SCLC. Initial efficacy data are encouraging. The hypothesis that high-dose once-daily TRT results in comparable or improved survival compared with twice-daily accelerated TRT warrants testing in a Phase III trial.