Abstract: Objective To compare the volumetric variations of target volume including gross tumor volume (GTV) and internal target volume (ITV) those were delineated in 3-dimensional (3D) and 4-Dimensional (4D) CT imaging. Methods Eight primary non-small cell lung cancer patients with 17 intrapulmonary solitary lesions and 4 patients with metastatic nodes received free-phase CT(FCT_0)at random respiratory phase and 4DCT scanning. 4DCT was reconstructed with 2-，3-，4-，5-，10- phase and maximal intensity projection (MIP) . For a single lesion, GTV was delineated in FCT_0 and various phases (GTV_x0, x=0, 1, 2, 3, 4, 5, 6, 7, 8, 9)in 4DCTs. FCT_x(x=0, 1, 2, 3, 4, 5)was expanded for the GTV in FCT with a margin of 1, 2, 3, 4, 5 mm. ITV_2(x=2, 3, 4, 5, 10)was composed of 2, 3, 4, 5 and 10 phases. The difference among the FCT_x, ITV_x and MIP was compared by paired t-test. Results Compared with the GTV in FCT, GTV_x0(x=0, 1, 2, 3, 4, 5, 6) in 4DCT was decreased by 21%-32% and GTV_x0 (x=7, 8, 9) by 7%-13% (P<0.05). The absolute and relative volume of FCT- x(x=0, 1, 2 3, 4, 5) was increased by 6-9 cm3 and 16%-31% respectively. As the additional margin were 1, 2，3, 4 and 5 mm, the GTV of FCT_1, FCT_2, FCT_3, FCT_4 and FCT_5 were increased 27%,68%,96%,141% and 198% respectively when comparing with that in GTV in FCT-0. ITV_x were significantly larger than MIP (P<0.05). When compared with MIP, the ITV was increased by 24%-54%. ITV-2 and ITV-3 were not significantly different to the MIP (P>0.05). ITV-4, ITV-5, and ITV-10, were significantly different to the MIP (P<0.05). Conclusion For a single intrapulmonary lesion, the target volume was significantly different in FCT and 4DCT which should be carefully taken into account during the design of radiation planning, especially in the stereotactic body radiotherapy.