| Purpose: Liver moves in three-dimensional direction with respiration and leads to descent of accuracy of target region in three-dimensional conformal radiotherapy (3DCRT). This study was designed to define individualized target volume which contain respiration movement using four-dimensional computed tomography (4DCT) , compare target volumes,displacement, exposure dose of normal tissue and the dose distribution between 3D plans and 4D plans,evaluate geometric and dosimetric advantage and investigate clinical significance of 4DCT on primary hepatocellular carcinoma(PHC). Methods: 3DCT and 4DCT scanning was obtained for 12 patients with primary hepatocellular carcinoma. 4DCT pictures comprise 10 respiratory phases of CT images.GTVs,CTVs,PTVs and normal tissues were contoured on 3DCT images. IGTVs,ITVs,IPTVs and normal tissues were contoured on 4DCT images. GTV was definite from tumor border on 3DCT images. IGTV encompassed all 10 GTVs on 4DCT images. CTV and ITV was derived from GTV and IGTV plus 0.8cm. PTV was derived from a single CTV plus conventional margins, which encompassed IM and SM. IPTV was derived from ITV, which encompassed all 10 CTVs plus SM. Using Xio treatment planning system to design two plans for each patient. The prescribed dose and design of irradiating fields were identical for both plans. Normal tissues were ensured to not exceeding the tolerance dose. The volumes and dose distribution of PTVs and IPTVs, the localization of GTVs and IGTVs, irradiated dose of normal livers were compared between the different plans.Results: The average PTV volume was 249.54±136.54cm~3. The average IPTV volume was 148.20±92.02cm~3. IPTV was less than PTV (101.34±63.87cm~3), P=0.000. Compared with GTVs, the migration of IGTVs was﹣0.23±1.37cm, 0.05±3.88cm,﹣0.12±0.71cm on X,Y,Z axial, but had no statistical significance. Dose distributions of 4D plans were better than 3D plans. Compared with 3D plans, the mean dose to normal liver (MDTNL) decreased from 18.81±3.89Gy to 14.59±4.47Gy, V23 decreased from 34.78±7.83% to 26.18±9.47%,V30 decreased from 30.21±7.30% to 22.95±9.28%, the normal tissue complication probability (NTCP) decreased from 12.72±9.27% to 6.46±6.69%,(P respectively are 0.000,0.000,0.001). Without increasing the normal tissue complication probability (NTCP). Conclusion: The conventional 3DCT can not locate the target region accurately, and then make 3DCRT hard to define the tumor volume precisely and result in geometric miss and include excess normal tissues. The 4DCT can record the tumor trace in respiratory movement, locate the target region precisely and avoid geometric lose. The 4DCT-based plans can definite individualized target volume, reduce the target volume to spare more normal tissues, especially normal liver, and make it possible to descend the NTCP, raise the dose of target region and increase the therapeutic effect of radiotherapy.
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