Simon Luc, Giraud Philippe, Servois Vincent, Rosenwald Jean-Claude
Institut Curie, Département de Radiothérapie, Paris, France.
J Appl Clin Med Phys. 2006 Nov 28;7(4):50-65. doi: 10.1120/jacmp.v7i4.2301.
A dynamic lung tumor phantom was used to investigate the geometric reconstruction accuracy of a commercial four-dimensional computed tomography (4D-CT) system. A ball filled with resin, embedded in a cork cube, was placed on a moving platform. Various realistic antero-posterior (AP) motions were programmed to reproduce the respiratory motion of a lung tumor. Several three-dimensional (3D) CT and 4D-CT images of this moving object were acquired and compared using different acquisition parameters. Apparent volume and diameter of the ball were measured and compared to the real values. The position of two points (the AP limits of the ball) during the motion in the coordinate system of the CT scanner were also compared with the expected values. Volume error was shown to increase with object speed. However, although the volume error was associated with intraslice artifacts, it did not reflect large interslice inconstancies in object position and should not be used as an indicator of image accuracy. The 3D-CT gave a random position of the tumor along the phantom excursion; accuracy in the assessment of position by 4D-CT ranged from 0.4 mm to 2.6 mm during extreme phases of breathing. We used average projection (AVE) and maximum intensity projection (MIP) algorithms available on the commercial software to create internal target volumes (ITVs) by merging gross tumor volume (GTV) images at various respiratory phases. The ITVs were compared to a theoretical value computed from the programmed ball excursion. The ITVs created from the MIP algorithm were closer to the theoretical value (within 12%) than were those created from the AVE algorithm (within 40%).
使用动态肺部肿瘤体模研究商用四维计算机断层扫描（4D-CT）系统的几何重建精度。将一个装满树脂的球嵌入软木立方体中，放置在移动平台上。编程了各种逼真的前后（AP）运动以重现肺部肿瘤的呼吸运动。采集了该移动物体的几张三维（3D）CT和4D-CT图像，并使用不同的采集参数进行比较。测量了球的表观体积和直径，并与实际值进行比较。还将CT扫描仪坐标系中运动过程中两点（球的AP边界）的位置与预期值进行了比较。结果表明，体积误差随物体速度增加。然而，尽管体积误差与层内伪影有关，但它并未反映物体位置的大的层间不一致性，不应用作图像准确性的指标。3D-CT给出了肿瘤在体模行程中的随机位置；在呼吸的极端阶段，4D-CT评估位置的准确性在0.4毫米至2.6毫米之间。我们使用商用软件上可用的平均投影（AVE）和最大强度投影（MIP）算法，通过合并不同呼吸阶段的大体肿瘤体积（GTV）图像来创建内部靶体积（ITV）。将ITV与根据编程的球行程计算出的理论值进行比较。与由AVE算法创建的ITV（误差在40%以内）相比，由MIP算法创建的ITV更接近理论值（误差在12%以内）。
