中文摘要：

目的探讨自由呼吸状态下四维CT（4DCT）测得的部分乳腺外照射（EBPBI）患者基于金属夹和血清肿所确定的术腔中心位移差异。方法在4DCT定位扫描EBPBI患者中选择血清肿可见度评分≥3者。在4DCT各时相图像上分别结合金属夹和血清肿及基于金属夹或血清肿勾画术腔并分别定义为GTVc＋s、GTVc、GTVs。标记术腔各边界金属夹并获得全部金属夹构成的几何体，测量并比较几何体、GTVc＋s、GTVc和GTVs中心及选定金属夹三维方向位移。结果几何体、GTVc＋s、GTVc、GTVs中心位移在左右方向分别为2．20、0．90、0．90、0．90mm，前后方向分别为1．80、1．20、1．05、1．05mm，上下方向分别为2．70、1．40、1．20、0．80mm。4个中心不同方向间均相似（X2=3．84～2．05，P=0．147～0．359），3个方向上几何体中心位移均大于GTVc＋s、GTVc。GTVs和选定金属夹位移（x2=15．38—21．022，P=0．000～0．002），上下方向上GTVc中心位移大于GTVs（Z=-2．05，P=0．041）。结论自由呼吸状态下金属夹构成的几何体中心各轴向位移均大于G1Vc＋s、GTVc、GTVs中心及选定金属夹位移，但GTVc＋s、GTVc、GTVs中心位移间差异并不明显。

英文摘要：

Objective To conduct a comparative study on the center displacement of surgical cavity delineated by metal clips and/or seroma on four-dimensional computed tomography （4DCT） in patients for external-beam partial breast irradiation （EBPBI） during free breathing. Methods Fourteen breast cancer patients, who had underwent breast-conserving surgery and met the requirements of EBPBI and who underwent 4DCT simulation scans and had a seroma clarity score of ≥3, were included in the study. On the 10 phases of 4DCT images, GTV8 were delineated based on metal clips plus seroma, metal clips, and seroma to obtain GTVc＋s, GTV0, and GTV＋, respectively, and all the metal clips at the boundaries of surgical cavity were marked to obtain the geometry. The three-dimensional center displacements of the geometry, GTV GTVc, and GTV＋ as well as four selected metal clips were measured and compared. Results The center displacements of the geometry, GTVc＋s, GTVc, and GTVs were 2.20, 0. 90, 0.90, and 0.90 mm, respectively, in the left-right （LR） direction, 1.80, 1.20, 1.05, and 1.05 mm, respectively, in the anterior-posterior （AP） direction, and 2.70, 1.40, 1.20, and 0. 80 mm, respectively, in the superior- inferior （SI） direction. For each of the geometry, GTVc＋s, GTVc, and GTVs, there were no significant differences between the center displacements in the LR, AP and SI directions （ X2 = 2.05 --3.84, P = 0. 147 --0. 359 ）. In each of the LR, AP and SI directions, the geometry had a significantly larger displacement than GTVc＋s、 GTVc, GTVs, and the four selected clips （ X2 = 15.38 --21. 022, P = 0. 000 -0. 002）. The center displacement of GTVo was larger than that of GTVs in the SI direction （Z = - 2. 05, P = 0. 041 ）. Conclusions During free breathing, the geometry consisted of all the metal clips has a larger center displacement than GTV GTVo, GTV＋, and the four selected metal clips in the LR, AP and SI directions, but there are no significant differences in center displacement between GT