Abstract: Objective：To discuss the significance of imageguided radiation therapy（IGRT） technique in measuring and correcting of target position errors in stereotactic body radiotherapy (SBRT) treatment for lung cancer. Methods：Totally 14 cases underwent SBRT treatment were enrolled in this study. Patients were scanned by kilovoltage cone beam CT (KVCBCT) before and after treatment, and online registered to the planning CT images; the target position error was corrected before treamtnet, and the CBCT was scanned and registered again after treatment. The target position errors were recorded before and after treatment. The CTVPTV margin was calculated by the formula 2.5Σ+0.7σ. Results：The maximum pretreatment error in rightleft, headfeet and backbelly directions were 10 mm, 16.9 mm and 8.7 mm,respectively. The mean value of target position errors in rightleft, headfeet and backbelly directions were (2.4±2.8) mm，(3.4±4.6) mm and (2.9±3.4)mm，respectively. The maximum posttreatment target position errors in rightleft, headfeet and backbelly directions after online correction were 7.6 mm，4.6 mm, and 7.0 mm, respectively, and the mean values were (2.1±2.0)mm，(1.5±1.6) mm and (1.7±2.0) mm，respectively. Without the usage of imageguide, the PTV margins in rightleft, headfeet and backbelly directions were 7.96 mm, 11.72 mm and 9.63 mm, respectively; with the usage of imageguide, the PTV margins in rightleft, headfeet and backbelly directions were 6.65 mm,4.87 mm and 5.65 mm, respectively. Conclusions：The IGRT technology can online correct the pretreatment target position errors and determine the target position removing during treatment. It can improve the treatment accuracy, and contribute to set the PTV margins.