Steep dose-response relationship for stage I non-small-cell lung cancer using hypofractionated high-dose irradiation by real-time tumor-tracking radiotherapy

PURPOSE: To investigate the clinical outcomes of patients with pathologically proven, peripherally located, Stage I non-small-cell lung cancer who had undergone stereotactic body radiotherapy using real-time tumor tracking radiotherapy during the developmental period. METHODS AND MATERIALS: A total of 41 patients (25 with Stage T1 and 16 with Stage T2) were admitted to the study between February 2000 and June 2005. A 5-mm planning target volume margin was added to the clinical target volume determined with computed tomography at the end of the expiratory phase. The gating window ranged from +/-2 to 3 mm. The dose fractionation schedule was 40 or 48 Gy in four fractions within 1 week. The dose was prescribed at the center of the planning target volume, giving more than an 80% dose at the planning target volume periphery. RESULTS: For 28 patients treated with 48 Gy in four fractions, the overall actuarial survival rate at 3 years was 82% for those with Stage IA and 32% for those with Stage IB. For patients treated with 40 Gy in four fractions within 1 week, the overall actuarial survival rate at 3 years was 50% for those with Stage IA and 0% for those with Stage IB. A significant difference was found in local control between those with Stage IB who received 40 Gy vs. 48 Gy (p = 0.0015) but not in those with Stage IA (p = 0.5811). No serious radiation morbidity was observed with either dose schedule. CONCLUSION: The results of our study have shown that 48 Gy in four fractions within 1 week is a safe and effective treatment for peripherally located, Stage IA non-small-cell lung cancer. A steep dose-response curve between 40 and 48 Gy using a daily dose of 12 Gy delivered within 1 week was identified for Stage IB non-small-cell lung cancer in stereotactic body radiotherapy using real-time tumor tracking radiotherapy.