基于锥形束CT与计划CT图像在线配准的非小细胞肺癌临床靶区外放研究

Study of defining an appropriate CTV-to-PTV margins for non-small cell lung cancer based on online registration of cone-beam CT images and planning CT images

目的 分析非小细胞肺癌（NSCLC）放疗过程中，应用锥形束CT（CBCT）图像在线校正或未进行在线校正时临床靶区（CTV）的合理外放。方法 8例行三维适形放疗的NSCLC患者入组。放疗前后各行CBCT扫描1次，并将CBCT图像与计划CT图像在线配准。根据配准获得的左右（X轴）、头脚（Y轴）、前后（Z轴）方向上平移矢量调整治疗床的位置，从而修正摆位和器官运动引入的误差。按上述方法每周采集CBCT图像2～3次。放疗前后配准得到的平移矢量分别作为分次间误差和分次内误差代入CTV外放计算公式，计算未进行在线校正和计算进行在线校正后NSCLC放疗的群体化CTV外放。结果 8例NSCLC患者共143组配准数据。若未进行CBCT在线校正，CTV外放为：左右方向8mm、头脚方向9mm、前后方向11mm。若进行CBCT在线校正，各方向上CTV外放均为2mm。结论NSCLC患者三维适形放疗时具有一定的摆位和器官运动误差。基于CBCT图像分析的在线校正方法能明显减小这些误差，并有助于确定合适的CTV外放。

Objective To estimate the appropriate margins for the clinical target volume（CTV） with or without online correction using cone-beam CT（CBCT） during the processs of radiation for non-small cell lung cancer（NSCLC） patients. Methods Eight patients with NSCLC treated with three-dimensional conformal radiotherapy（3D-CRT） were investigated, kV CBCT scans were performed before and immediately after radiotherapy. Then analysis of these images was performed using automatic and manual registration of the CBCT and planning computed tomography images. The patient positioning and organ motion were corrected by moving the couch in the left- right （X） , craniocaudal （Y） , and anterior- posterior （ Z ） directions accordingly, and CBCT online-guided correction data were recorded. The clinical study performed 2-3 times per week. CBCT data acquired before treatment delivery were used to evaluate the positioning error and organ motion, and that acquired after treatment were used to assess intrafraction tumor displacement and organ motion. These data were used in a standard formula to calculate CTV-to-PTV（ planning target volume） margin of online-guided correction and non-online-guided correction. Results Total of 143 sets of CBCT images were analyzed. On the condition of non-correction, the margins required to account for total errors were 8 mm, 9 mm, 11 mm in X, Y and Z directions respectively. When the tumor was corrected every fraction, margins required to account for intrafraction errors were 2 mm in each directions. Conclusion There are some extent of errors from positioning and organ motion in 3D-CRT for NSCLC. Online correction approach based on CBCT images analysis can be used to reduce the impact obviously and to estimate the appropriate margins for the CTV.