Objectives: We investigated the performance of a slow computed tomography (CT) protocol to reduce alignment errors arising from motion when using CT-on-rail (CTOR) for image guidance for patients receiving thoracic stereotactic body radiation therapy (SBRT).Methods: A Quasar lung phantom with a moving tumor was programmed with three breathing rates and three motion amplitudes. MIP and average 4DCT images were used for contouring and alignment, respectively. Ten CTOR images were obtained for each of the breathing rates and amplitudes, under both CT protocols. We used in-house CAT software for image guidance, centering the tumor in the lung window within the gross tumor volume contour. Longitudinal coordinate reproducibility was compared between the two protocols. We also retrospectively analyzed CBCT SBRT image guidance alignment data from 31 patients to evaluate the systematic error in the longitudinal direction between simulation and daily treatments.Results: The mean (standard deviation) alignments (mm) for the standard and slow CT protocol ranged from 0.7 (0.68) and 1.0 (0.0), respectively, for the 28 BPM breathing rate and 5 mm amplitude combination to 5.2 (2.0) and 1.6 (0.52) for the 8 BPM breathing rate and 15 mm amplitude combination. Our retrospective analysis of patient alignment data showed a notable systematic difference in the relative bone and gross tumor volume alignment between the simulation and daily cone beam CT datasets. The mean longitudinal difference was −0.19 cm (standard deviation, 0.17 cm; range, 0.28 cm to −1.14 cm). Therefore, the position of the vertebral body cannot be used as a surrogate for mean tumor position in the longitudinal direction. Longitudinal position must be accurately determined for each patient using multiple CT images.Conclusions: A slow CT protocol improved the alignment with slower breathing rates being more challenging. A 5 mm PTV is not sufficient for tumor motion greater than 9 mm. Averaging the coordinates from multiple CTOR images is recommended.
目的：本研究旨在评估一种慢速计算机断层扫描（CT）方案在降低胸段立体定向体部放射治疗（SBRT）患者使用导轨CT（CTOR）进行图像引导时，因呼吸运动引起的配准误差方面的性能。 方法：使用内置运动肿瘤的Quasar肺部模体，设定三种呼吸频率与三种运动幅度组合。分别采用最大密度投影（MIP）和平均四维CT（4DCT）图像进行靶区勾画与配准。在标准与慢速两种CT协议下，对每种呼吸参数组合各采集十组CTOR图像。采用自主研发的CAT软件进行图像引导，将肿瘤置于大体肿瘤体积轮廓内的肺窗中心。比较两种协议在纵向坐标重复性上的差异。同时回顾性分析31例患者的锥形束CT（CBCT）SBRT图像引导配准数据，评估模拟定位与每日治疗间纵向方向的系统误差。 结果：在28次/分钟呼吸频率配合5毫米运动幅度条件下，标准与慢速CT协议的平均（标准差）配准误差（毫米）分别为0.7（0.68）和1.0（0.0）；而在8次/分钟呼吸频率配合15毫米运动幅度条件下，两者误差分别为5.2（2.0）和1.6（0.52）。患者配准数据的回顾性分析显示，模拟定位与每日锥形束CT数据集在骨性结构与大体肿瘤体积的相对配准间存在显著系统差异。纵向平均差异为-0.19厘米（标准差0.17厘米；范围0.28厘米至-1.14厘米）。因此，椎体位置不能作为肿瘤纵向平均位置的替代参考指标，必须通过多幅CT图像为每位患者精确确定纵向位置。 结论：慢速CT协议能改善配准精度，其中较低呼吸频率的挑战性更大。当肿瘤运动幅度超过9毫米时，5毫米的计划靶体积边界不足。建议通过多幅CTOR图像的坐标取平均值以提高定位准确性。
肿瘤(癌症)患者之家