Objective To use the fusion image of the end-inhalation holding (EIH) phase and endexhalation holding (EEH) phase to define the target volume of individual patient with liver cancer,and to evaluate the target geometry,feasibility,and clinical significance of the technology.Methods Eighteen patients with liver caucer who were treated in our hospital from 2012 to 2013 were enrolled as subjects.With the same posture and scan range,all patients underwent contrast-enhanced three-dimensional computed tomography (3DCT) scans in the phases of free breathing (FB),EIH,and EEH.Gross tumor volume (GTV),clinical target volume (CTV),and organ of risk (OAR) were delineated on the above images.CTVFB was defined as GTV on the FB phase image (GTVFB) plus a margin of 10 mm,while planning target volume (PTVFB) was defined as CTVFB plus a margin of 10 mm in the right-left and anterior-posterior directions and a margin of 20 mm in the superior-inferior direction.GTVEI and GTVEE were defined as GTV on the EIH and EEH images,respectively.Based on the EEH images,the registered EEH and EIH images were fused to form GTVEI+EI.CTVEI+EE was defined as GTVEI+EI plus a margin of 10 mm,while PTVEI+EE was defined as CTVEI+EE plus a margin of 5 mm in the right-left and anterior-posterior directions and a margin of 10 mm in the superior-inferior direction.The Pinnacle3 v8.0m treatment planning system was used to design two 3D conformal radiotherapy plans for each patient.The volume,degree of inclusion (DI),matching index (MI),and central displacement of CTVFB and CTVEI+EE,as well as PTVFB and PTVEI+EE,were compared between the two plans.Results In the 18 patients,the mean CTVFB was significantly smaller than the mean CTVEI+EE(149.00±87.54 cm3 vs.188.17± 125.72 cm3,P=0.014);there was no significant difference between the mean PTVFB and PTVEI+EE (276.68± 146.41 cm3 vs.253.66± 117.35 cm3,P=0.080).DI of CTVFB to CTVEI+EF,PTVFB to PTVEI+EE,CTVEI+EE to CTVFB,and PTVEI+EE to PTVFB were (99.83±0.09)％,(84.55±8.45) ％,(80.83± 12.31) ％,and (99.78±0.08) ％,respectively.MI of CTVEI+EE to CTVFB and PTVEI+EE to PTVFB were 0.83± 0.07 and 0.87± 0.03,respectively.The central displacements of CTVEI+EE from CTVFB in x,y,and z axes were 0.55± 1.07 cm,0.76±3.02 cm,and-0.26± 1.98 cm,respectively (P =0.432,0.971,0.587).Conclusions In the treatment of liver cancer,the target volume delineation and image fusion using 3DCT images in EIH and EEH phases may avoid target omission due to respiratory movement,making it possible to increase radiation dose to target volume and improve the efficacy of radiotherapy.