肺肿瘤在线与离线结合锥形束CT图像引导放疗的可行性研究

Feasibility study of image guided radiotherapy for lung tumor using online and offiine cone-beam CT setup verification

目的探讨肺肿瘤在、离线结合锥形束CT（CBCT）图像引导放疗的可行性。方法14例行三维适形放疗的肺肿瘤患者入组。放疗前后分别行在线CBCT扫描1次，并与计划CT图像配准，记录各个方向的配准差值。放疗前后配准获得的平移矢量分别作为分次间误差和分次内误差，利用CTV外放公式分别计算未行在线校正以及在线校正后的CTV外放。分别以0．5、1．5mm为允许的最大残余系统摆位误差，计算预测总系统摆位误差所需的最少CBCT图像数以及离线校正系统摆位误差后的CTV外放。结果未行在线校正时，左右、头脚、前后方向上群体化CTV外放分别为5．7、8．0、7．8mm；每分次放疗均行在线校正时，3个方向上群体化CTV外放分别为2．4、2．4、2．3mm。分别以0．5mm或1．5mm为允许的最大残余系统误差，计算预测系统摆位误差所需的最少CBCT图像数为9套或7套，对系统摆位误差进行离线校正后，左右、头脚和前后方向上群体化CTV外放分别为3．3mm或3．9mm、3．7mm或4．3mm和3．6mm或4．3mm。结论基于CBCT图像分析的在线校正和离线校正均能明显减小摆位误差，并有助于缩小CTV外放。肺肿瘤患者进行在线、离线相结合的图像引导放疗是可行的。

Objective To investigate the feasibility of online and offline cone-beam CT （CBCT） guided radiotherapy for lung cancer. Methods Fourteen patients with lung tumor treated by three-dimensional conformal radiotherapy were investigated. Online kV CBCT scan,image registration and setup correction were performed before and immediately after radiotherapy. CBCT online-guided correction data were used to calculate the population-based CTV-PTV margins under the condition of non-correction and correction in every fraction respectively. The numbers of initial images and the population-based CTV-PTV margins after the offline compensation of the system setup error were evaluated with the permission of 0.5 mm and 1.5 mm maximal residue error,respectively. Results Under the condition of non-correction,the required margins for total error were 5.7 mm,8.0 mm and 7.8 mm in the left-right（x axis） ,cranio-caudal（y axis） and anterior-posterior（z axis） directions, respectively. When the tumor was corrected in every fraction, the required margins for intra-fraction error were 2.4 mm,2.4 mm and 2.3 mm in x, y and z axes, respectively. To correct the systematic setup error,9 sets of CBCT images for 3.3 mm,3.7 mm and 3.6 mm PTV margins, and 7 sets of CBCT images for 3.9 mm,4.3 mm and 4.3 mm PTV margins in x,y and z axes were necessary when 0.5 mm and 1.5 mm maximal residue errosr were permited respectively. Conclusions Both of the online CBCT correction and the offline adaptive correction can markedly reduce the impact of setup error and reduce the required PTV margins accordingly. It is feasible to deliver the online and offline image guided radiation for patients with lung tumor.