4D-CT联合锥形束CT在肺癌放疗中靶区外放边界的研究

Study of Four-Dimensional CT Combined with Cone-Beam CT on the Target Margin of Lung Cancer Radiotherapy

目的 分析四维CT(Four-Dimensional Computed Tomography,4D-CT)联合锥形束CT(Cone-Beam CT,CBCT)对肺癌放疗中因呼吸运动和摆位误差对靶区外放值的影响,为临床靶区勾画提供参考。方法 选取2020年7月至2022年9月在安徽医科大学第一附属医院接受4D-CT扫描的肺癌放疗患者24例,其中采用呼吸门控技术患者12例,未采用呼吸门控技术患者12例。所有患者定位时进行4D-CT扫描,且首次放疗前行CBCT扫描,之后每周行CBCT扫描,其中采用呼吸门控治疗患者每次治疗前均行CBCT扫描,采用肿瘤中心点在4D-CT图像中10个时相上的位移作为影响呼吸运动的参数,并结合CBCT的位移数据计算靶区外放边界值,分析肿瘤中心点位置、摆位误差以及肿瘤中心点三维方向上相关性。结果 24例患者随呼吸运动肿瘤中心点在左右、头脚、前后方向上的位移分别为(0.21±0.20)、(0.52±0.49)、(0.29±0.21)cm。摆位误差在左右、头脚、前后方向上的位移分别为(0.06±0.31)、(-0.06±0.46)、(0.07±0.36)cm。仅利用摆位误差只能得出内在靶体积到计划靶区的外放边界值,在3个方向上最大值分别为0.36、0.47、0.43 cm。利用肿瘤中心点位移和摆位误差位移得出肿瘤靶区外放边界3个方向最大值分别为0.73、1.31、0.82 cm。结论 4D-CT联合CBCT能减小肺癌患者放疗中的靶区外放,利用呼吸门控在4D-CT计划基础上也可进一步精确靶区外扩边界。

Objective To analyze the impacts on the external release value of target volume due to respiratory movement and setup errors in radiation therapy for lung cancer with the help of four-dimensional computed tomography(4D-CT)combined with cone-beam CT(CBCT),to provide a reference for clinical target volume delineation.Methods A total of twenty-four lung cancer patients who received 4D-CT scanning and radiation therapy from July 2020 to September 2022 in The First Affiliated Hospital of Anhui Medical University were selected,among which twelve patients were treated with respiratory gating technique and twelve patients were treated without respiratory gating technique.All patients underwent 4D-CT scanning during localization,and underwent CBCT scanning before the first radiotherapy,and then underwent CBCT scanning weekly.Among them,patients treated with respiratory gating underwent CBCT scanning before each treatment.The displacement of the tumor center at ten-time phases of the 4D-CT image was used as the parameter affecting the respiratory movement,and the margin value of target volume was calculated in combination with the displacement data of CBCT.Analyzed the position and setup errors of the tumor center point,as well as the correlation in the three-dimensional direction of the tumor center point.Results In the 24 patients with respiratory movement,the displacement of tumor center point in the directions of left-right,superior-inferior,and anterior-posterior were(0.21±0.20),(0.52±0.49)and(0.29±0.21)cm,respectively.The displacement of setup errors in left-right,superior-inferior,and anterior-posterior directions were(0.06±0.31),(-0.06±0.46)and(0.07±0.36)cm,respectively.Only by using the setup error,the external boundary value from internal target volume to planning target volume can be obtained,and the maximum values in the three directions are 0.36,0.47 and 0.43 cm,respectively.Using the displacement of the tumor center point and the displacement of the setup errors,the maximum values of the three directions of the tumor target area were 0.73,1.31,and 0.82 cm,respectively.Conclusion 4D-CT combined with CBCT can reduce the target margin in the radiotherapy for lung cancer patients,and the use of respiratory gating based on 4D-CT plan can also further accurately expand the target margin.