Abstract： Objective To study the value of image-guided radiotherapy (IGRT) in lung cancer. Methods From Mar. 2007 to Dec. 2007,58 patients with lung cancer were treated with IGRT. Set-up er-rors in each axial direction was calculated based on IGRT images of each patient. The change of GTV was e-valuated on both cone-beam CT and CT simulator images. Results Twenty-two patients with left lung cane-er,30 with right lung cancer,5 with mediastinal lymphanode metastasis and one with vertebra metastasis were included. The set-up error in x,y and z axes was (0.02±0.26) cm, (0.14±0.49) cm and ( -0. 13± 0.27) cm, respectively,while the rotary set-up error in each axis was -0.15°± 1.59°, -0.01°± 1.50° and 0.12°±1.08°, respectively. The set-up errors were siguifieantly decreased by using of IGRT. GTV movement was observed in 15 patients (25.9%) ,including 5 with left upper lung cancer. GTV moving to the anterior direction was observed in 9 patients,including 4 with]eft upper lung cancer. GTV reduced in 23 (44.2%) patients during treatment. Asymmetric GTV reduction of 22 lesions was observed,with a mean re-ductive volume of 4.9 cm3. When GTV began to shrink,the irradiation dose was 4 -46 Gy,with 20 -30 Gy in 9 patients. Conclusions The use of IGRT can significantly reduce set-up errors. GTV movement and reduction are observed in some cases. The time to modify the target volume needs to be further studied.