四维CT测定保乳术后部分乳腺外照射术腔中银夹的位移

Displacement of the silver clips in surgical cavity based on four-dimensional CT images for patients undertaking external.beam partial breast irradiation after breast-conserving surgery

目的探讨四维CT（4D—CT）模拟定位影像所测得的保乳术后术腔中银夹和银夹所构成的几何体中心点位移在确定部分乳腺外照射（EB-PBD内靶区中的价值。方法14例保乳术后拟行EB-PBI的患者，在自由呼吸状态下行大孔径CT模拟定位，并获得4D-CT图像。在治疗计划系统中，分别勾画10个呼吸时相CT图像上术腔中选定银夹并标记术腔中全部银夹，获得选定银夹和所有银夹构成几何体中心点在左右、前后和上下三维方向上的位移，进行差异性与关联性比较。结果同一选定银夹在前后和上下方向上的位移明显大于左右方向（均P〈0．05）；除最外侧与最下层银夹的上下方向外，其他选定银夹在同一方向上的位移差异均无统计学意义（均P〉0．05）。几何体中心点在左右、前后和上下方向上的位移分别为（1．34±0．39）mm、（2．01±1．02）mm和（1．89±1．03）mm，左右与前后以及左右与上下方向上的位移差异均有统计学意义（均P〈0．05）；在左右、前后和上下方向上，几何体中心点的位移均大于各选定银夹在同一方向上的位移，除上下方向外，差异均有统计学意义（均P〈0．05）。在上下方向上，几何体中心点的位移与最上层银夹及最下层银夹的位移相关（均P〈0．05）。结论以4D—CT模拟定位图像进行EB—PBI靶区确定时，术腔中各边界选定银夹位移不能代替基于术腔中全部银夹所确定的EB—PBI靶区位移。

Objective To explore the displacement of the selected clips and the center of the geometry consisted of all the clips in the surgical cavity measured on the basis of four-dimensional computed tomography （4D-CT） simulation images. Methods Fourteen breast cancer patients after breast-conserving surgery were recruited for external beam partial-breast irradiation （EB-PBI） , and received large aperture CT simulation. The 4D-CT image data sets were collected when the patient was in the free breathing state. Using the Varian Eclipse treatment planning system, the selected four clips in the cavity were separately delineated on the CT images from 10 phases of the breath cycle, and all of the clips in the cavity were marked to obtain the geometry. Then the displacement of the four selected clips and the center of the geometry in the left-right （ LR）, anterior-posterior （AP） , and superior-inferior （SI） directions were measured. The differences of the displacement were compared. Results The displacements in the AP and SI directions were always greater than the displacement in LR direction for the same selected clip. The difference of the displacements in the same direction of the different selected clips was not statistically significant （ P 〉 0.05 ）. The displacements of the geometry center consisted of all of the clips in the LR, AP, SI directions were （ 1.34 ± 0.39） mm, （ 2.01 ±1.02 ） mm and （ 1.89±1.03 ） mm, respectively, and the difference of the displacements between LR and AP, LR and SI were all statistically significant （P 〈 0.05 ）. In the same directions （LR, AP and SI）, the displacement of geometry center was always greater than the displacement of the selected clips, and the difference except SI direction was all statistically significant （ P 〈 0.05 ）. In the SI direction, the association between the displacement of geometry center and the upper clip, geometry center and the lower clip was statistically significant （ P 〈 0.05 ）. Conclusion When the target for EB-PBI is defined on the basis of 4D-CT simulation images, the displacement of the selected clips at the border of the surgical cavity is not qualified to substitute the displacement of the target defined basing on all of the clips in the surgical cavity.