Department of Radiation Oncology and Medical Physics, Sapporo Medical University Graduate School of Medicine, Sapporo, Japan.
J Appl Clin Med Phys. 2012 Mar 8;13(2):3715. doi: 10.1120/jacmp.v13i2.3715.
We aimed to optimize internal margin (IM) determination for respiratory-gated radiotherapy using end-expiratory phase assessments using a motion phantom. Four-dimensional computed tomography (4D CT) data were acquired using a GE LightSpeed RT CT scanner, a respiratory-gating system, and a motion phantom designed to move sinusoidally. To analyze the accuracy of 4D CT temporal resolution, a 25.4 mm diameter sphere was inserted into the motion phantom, and we measured the differences in sphere diameters between static and end-exhalation phase images. In addition, the IM obtained from the maximum intensity projection within the gating window (MIP(GW)) image was compared to theoretical value. Cranial-caudal motion displacement ranged from 5.0 to 30.0 mm, and the respiratory period ranged from 2.0 to 6.0 sec. Differences in sphere diameters between static and end-exhalation phase images ranged from 0.37 to 4.6 mm, with 5.0-mm and 30 mm target displacements, respectively. Differences between the IM obtained from the MIP(GW) and the theoretical values ranged from 1.12 to 6.23 mm with 5.0mm and 30 mm target displacements, respectively. These differences increased in proportion to the target velocity due to a motion artifact generated during tube rotation. In this study, the IMs obtained using the MIPGW image were overestimated in all cases. We therefore propose that the internal target volume (ITV) for respiratory-gated radiotherapy should be determined by adding the calculated value to the end-exhalation phase image. We also demonstrate a methodology for subtracting motion artifacts from the ITV using a motion phantom.
我们旨在使用呼吸门控放疗末期相位评估，通过运动体模优化内部靶区（IM）的确定。使用通用电气 LightSpeed RT CT 扫描仪、呼吸门控系统和设计成正弦运动的运动体模采集四维 CT（4D CT）数据。为了分析 4D CT 时间分辨率的准确性，将一个 25.4 毫米直径的球体插入运动体模中，我们测量了静态和呼气末期相位图像之间的球体直径差异。此外，将门控窗（MIP(GW))图像内的最大强度投影（MIP(GW))图像中的 IM 与理论值进行比较。头脚方向的运动位移范围为 5.0 至 30.0 毫米，呼吸周期范围为 2.0 至 6.0 秒。静态和呼气末期相位图像之间的球体直径差异范围为 0.37 至 4.6 毫米，分别对应 5.0 毫米和 30 毫米的靶标位移。MIP(GW)图像获得的 IM 与理论值之间的差异范围为 1.12 至 6.23 毫米，分别对应 5.0 毫米和 30 毫米的靶标位移。由于管旋转时产生的运动伪影，这些差异与目标速度成比例增加。在这项研究中，使用 MIPGW 图像获得的 IM 在所有情况下都被高估了。因此，我们建议在呼吸门控放疗中，应通过将计算值添加到呼气末期相位图像来确定内部目标体积（ITV）。我们还展示了一种使用运动体模从 ITV 中减去运动伪影的方法。
