Sillanpaa J, Chang J, Mageras G, Riem H, Ford E, Todor D, Ling C C, Amols H
Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021, USA.
Med Phys. 2005 Mar;32(3):819-29. doi: 10.1118/1.1861522.
We have studied the feasibility of a low-dose megavoltage cone beam computed tomography (MV CBCT) system for visualizing the gross tumor volume in respiratory gated radiation treatments of nonsmall-cell lung cancer. The system consists of a commercially available linear accelerator (LINAC), an amorphous silicon electronic portal imaging device, and a respiratory gating system. The gantry movement and beam delivery are controlled using dynamic beam delivery toolbox, a commercial software package for executing scripts to control the LINAC. A specially designed interface box synchronizes the LINAC, image acquisition electronics, and the respiratory gating system. Images are preprocessed to remove artifacts due to detector sag and LINAC output fluctuations. We report on the output, flatness, and symmetry of the images acquired using different imaging parameters. We also examine the quality of three-dimensional (3D) tomographic reconstruction with projection images of anthropomorphic thorax, contrast detail, and motion phantoms. The results show that, with the proper choice of imaging parameters, the flatness and symmetry are reasonably good with as low as three beam pulses per projection image. Resolution of 5% electron density differences is possible in a contrast detail phantom using 100 projections and 30 MU. Synchronization of image acquisition with simulated respiration also eliminated motion artifacts in a moving phantom, demonstrating the system's capability for imaging patients undergoing gated radiation therapy. The acquisition time is limited by the patient's respiration (only one image per breathing cycle) and is under 10 min for a scan of 100 projections. In conclusion, we have developed a MV CBCT system using commercially available components to produce 3D reconstructions, with sufficient contrast resolution for localizing a simulated lung tumor, using a dose comparable to portal imaging.
我们研究了低剂量兆伏级锥形束计算机断层扫描（MV CBCT）系统在非小细胞肺癌呼吸门控放射治疗中可视化大体肿瘤体积的可行性。该系统由一台商用直线加速器（LINAC）、一个非晶硅电子射野成像装置和一个呼吸门控系统组成。使用动态束流输送工具箱（一种用于执行控制直线加速器脚本的商业软件包）来控制机架运动和束流输送。一个专门设计的接口箱使直线加速器、图像采集电子设备和呼吸门控系统同步。对图像进行预处理以消除由于探测器下垂和直线加速器输出波动产生的伪影。我们报告了使用不同成像参数获取的图像的输出、平整度和对称性。我们还使用人体胸部投影图像、对比细节和运动体模检查了三维（3D）断层重建的质量。结果表明，通过适当选择成像参数，每个投影图像低至三个束流脉冲时，平整度和对称性相当好。在使用100次投影和30 MU的对比细节体模中，可以分辨5%的电子密度差异。图像采集与模拟呼吸的同步也消除了运动体模中的运动伪影，证明了该系统对接受门控放射治疗患者进行成像的能力。采集时间受患者呼吸限制（每个呼吸周期仅一幅图像），扫描100次投影的时间不到10分钟。总之，我们使用商用组件开发了一种MV CBCT系统，以产生三维重建，具有足够的对比分辨率来定位模拟的肺部肿瘤，使用的剂量与射野成像相当。
