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[目的]利用影像质控体模,测量三种型号的TPS/CT-Sim工作站在不同CT扫描参数时图像重建的几何结构和射野设置的精度,以及CT值的改变范围。[方法]质控体模内置15种不同形状、大小和密度的模块,体积大小范围为0.5cc～125.0cc,相对电子密度为0.190～1.512,在CT模拟机扫描后输入到各TPS/CT-Sim工作站进行影像重建测试。测试条件分为6组不同的扫描参数。比较各系统在不同扫描条件下的影像重建质量、计划设计的几何精度及CT值与相对电子密度的改变。[结果]不同TPS/CT-Sim工作站的影像重建均存在不同程度的偏差(-27%～27.4%);CT扫描参数对各系统的影像重建体积有明显的影响,扫描层厚和螺距对重建体积的影响较其他因素显著;层厚扫描为3mm及扫描螺距为1.0时,各系统图像重建体积误差较小;CT扫描电压和电流对图像重建体积的影响不明显但会使CT值产生明显差异。[结论]各放疗单位有必要对临床使用的每台TPS/CT-Sim和CT扫描参数进行影像质量检测和评估,以决定适合具体系统的使用条件和误差范围;在使用体积剂量工具进行治疗计划评估时应考虑影像重建体积的误差。
[Objective] The purpose of this study was to measure the geometrical structure of image reconstruction and the accuracy of field setting and the scope of CT value changes of three types of TPS / CT-Sim workstations under different CT scanning parameters by using image quality control phantom. [Method] The control phantom incorporates 15 kinds of modules of different shapes, sizes and densities with the volume ranging from 0.5 cc to 125.0 cc and the relative electron density ranging from 0.190 to 1.512. After the CT simulator scans, it is input to each TPS / CT- Sim workstation for image reconstruction test. Test conditions are divided into 6 groups of different scanning parameters. The quality of image reconstruction, the geometrical accuracy of planning and the change of CT value and relative electron density of each system under different scanning conditions were compared. [Results] The image reconstructions of different TPS / CT-Sim work stations had different degrees of deviation (-27% -27.4%). The CT scan parameters had a significant effect on the volume of image reconstruction of each system. Volume of the image is more significant than other factors. When the thickness of the layer is 3mm and the scanning pitch is 1.0, the volume error of each system image reconstruction is small. The effect of CT scanning voltage and current on the image reconstruction volume is not obvious but the CT value will be significantly different . [Conclusion] It is necessary for radiotherapy units to detect and evaluate the image quality of each TPS / CT-Sim and CT scan parameters used clinically in order to decide the conditions of use and the error range suitable for the specific system. When using the volume dose tool for treatment planning The evaluation should take into account the error of the image reconstruction volume.