| Background and Objective: Four-dimensional CT (4D-CT) has been considered as a reliableand effective tool for assessing tumor and organ motion.4D-CT images can eliminate the motionartifacts of clips caused by respiratory motion, therefore they can accurately reflect clip motionthroughout the respiratory cycle. Comparing with the three-dimensional CT (3D-CT), the4D-CTcontains more motion information and the positional variation of the target volume. So we designthis study to explore the following projects：(1)This study investigated the displacement of the clipin surgical cavity based on the4D-CT for patients after breast-conserving surgery and thedisplacement of the geometric center consisting of all the clips and its association with thedisplacement of the selected clips to define the internal target volume (ITV).(2)This study alsoinvestigated the differences of clinical target volume (CTV) delineated on3D-CT and4D-CT of thewhole breast after breast-conserving surgery by comparing of the breast volumetric and the relatedparameters of the CTV based on3D-CT and4D-CT.Methods and Materials: Fourteen breast cancer patients after breast-conserving surgeryunderwent big bore3D-CT and4D-CT simulation scan of the thorax during free breathing.(1) InVarian Eclipse treatment planning system, the selected four clips in the cavity were separatelydelineated on the CT images from ten phases of breath cycle and all of the clips in the cavity weremarked to obtain the geometry consisted of all of the clips, then the displacement of the four selected clips and the center of the geometry at left-right (LR), anterior-posterior (AP) andsuperior-inferior (SI) directions were measured. The differences of the displacement of the sameselected clip at three-dimensional directions, the difference of the displacement of the differentselected clips at the same direction, and the difference and associativity between the difference ofthe selected clips and the geometry center were compared.(2).Selected the case of thirteen cases,The CTVs were delineated on the3D-CT images,4D-CT images and the maximum intensityprojections(MIP) images by the same radiation oncologist. The CTV3D, CTV0, CTV20, CTV50andCTVMIPwas defined on the3D-CT, T0, T20, T50, MIP images and all the CTV delineated on theimages from ten phases of the4D-CT were fused into an ICTV. The volumes of the CTVS, thematching index (MI) and the degree of inclusion (DI) were compared respectively.Results:1. Displacements of the clip and the geometry center(1). The displacements of AP and SI were always greater than the displacement of LR for thesame selected clip. The difference of the displacement at the same direction of the different selectedclip was not statistically significant (P>0.05).(2). The displacements of center of the geometry consisted of all of the clips in the direction ofLR, AP, SI were （1.34±0.39）mm,（2.01±1.02）mm and（1.89±1.03）mm，respectively, andthe difference of the displacement between LR and AP, LR and SI were all statistically significant(P<0.05). At the same direction of LR, AP and SI, the displacement of geometry center was alwaysgreater than the displacement of the selected clips, and the difference except SI direction were allstatistically significant (P<0.05). At SI direction, the associativity between the displacement ofgeometry center and upper clip, geometry center and lower clip were statistically significant(P<0.05).2. Comparison of the whole breast target delineated on3D-CT and4D-CT(1). There is no difference in the CTV delineated by the same oncologist（P＞0.05）.(2). The comparison of the volume between CTV3Dand CTV0, CTV20, CTV50, CTVMIPdemonstrated no significant difference (Z=-1.255~-0.267, P=0.209~0.790). DI of CTV3Din CTV0,CTV20, CTV50were93.25%,92.82%,92.41%, respectively. DI of CTV0, CTV20, CTV50in CTV3D were93.53%,93.73%,93.18%, respectively. There is no significant difference between the DI ofCTV3Din CTV of the single phases of4D-CT and the DI of CTV of the single phases in CTV3D（Z=-0.941,-1.255,-1.177; P=0.347,0.209,0.237）. The MI between CTV3Dand CTV0, CTV20,CTV50were0.87±0.04,0.87±0.04,0.86±0.04, respectively. The difference of the MI of theCTV of4D-CT and CTV3Dinduced by respiration motion was not statistically significant (F=0.326, P=0.724).(3). The volume of the ICTV was larger than that of CTV3D（Z=-3.061, P=0.002）and thediference of the DI in each other was significant（Z=-3.059, P=0.002）. The MI between CTV3Dand ICTV was0.86±0.04. A significant difference was found between the volume of the ICTV vs.CTVMIP(Z=-3.059, P=0.002) and the difference of the DI in each other was significant（Z=-2.936, P=0.003）. The MI of ICTV and CTVMIPwas0.94±0.02.Conclusions:1. Displacements of the clip and the geometry center(1). No matter what selected clips or geometry consisted of all of the clips in the surgicalcavity, the displacement in LR direction was always statistically significantly less than that in APand SI directions.(2). When the target for patients after breast-conserving surgery was defined basing on4D-CTsimulation images, the displacement of the selected clips at the border of the surgical cavity was notqualified to substitute the displacement of the target defined basing on all of the clips in the surgicalcavity.2. Comparison of the whole breast target delineated on3D-CT and4D-CT(1). When the whole breast target of breast cancer were delineated on the3D-CT images,4D-CT images and the MIP images by the same oncologist, there was no obvious difference in thewhole breast target at different time under the same criterion of target delineation.(2). There was no difference between the whole breast target delineated on the3D-CT imagesand image of the single phase in4D-CT or MIP images. Meanwhlie, the space overlap ratio ofwhole breast target were quitely high either the whole breast target delineated on the3D-CT imagesand images of the single phases in4D-CT or the3D-CT images and MIP images analysed by the DI and MI.(3). The space overlap ratio and the volume of whole breast target delineated on the3D-CTimages were always significantly less than that of ICTV. |
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