Objective To explore the influence of different reconstruction modes with time?weighted respiratory phases on the internal tumor volume ( ITV) of solitary pulmonary lesion ( SPL) , and to evaluate the feasibilities of 8 and 4 equal time?weighted respiratory phases in 4DCT simulation. Methods 24 patients with SPL underwent 4D scanning. Images were reconstructed with 10, 8 and 4 equal time?weighted phases of the respiratory cycles, respectively. Gross tumor volumes ( GTVs ) were delineated on the three sets of reconstructed images and fused into ITVs, which were ITV10 , ITV8 and ITV4 respectively. The differences of volumes, centroid of the ITVs and motions of GTV centroids in three?dimensional directions were compared. Statistical analysis was performed using the Friedman M test. Results The volumes of ITV10 , ITV8 and ITV4 were (9.09±12?29) cm3,(9.10±12?47) cm3 and (8.98±12?61) cm3(P=0?001), respectively. There were no differences between the volumes of ITV10 and ITV8 after the Bonferroni correction ( P=0?721) , while the opposite between those of ITV10 and ITV4 ( P=0?002 ) . The differences of centroid positions of ITV10, ITV8 and ITV4 in x?, y?and z?axes were all less than 1 mm ((12.22±7?71),(12.23± 7?71),(12.22±7?71),Px =0?668);(43.30±29?38),(43.30±29?40),(43.31±29?39),Py =0?643;(5.66±3?67),(5.66±3?67),(5.66±3?67),Pz=0?878), similar to the motions of GTV centroids in three reconstructed modes ((0.69±0?56),(0.69±0?68),(0.79±0?51) mm,Px=0?356;(3.13±3?78),(3.13± 4?05),(3.19±4?06) mm,Py =0?978;(1.18±1?31),(1.03±1?32),(1.16±1?34) mm,Pz=0?302). Conclusions There were no differences in volumes, centroid positions and motions between ITV10 and ITV8 . The quantity of reconstruction images and GTV delineations according to 8 time?weighted phases were both less than conventional 10 phases. 8 time?weighted respiratory phases mode was feasible in 4DCT simulation for SPL.