Mawatari Shinji, Oku Yoshifumi, Toyota Masahiko
Department of Radiology, Division of Clinical Technology, Kagoshima University Hospital.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2025;81(12). doi: 10.6009/jjrt.25-1562.
Cone beam computed tomography (CBCT) is the most commonly used technique for target localization in radiation therapy. Four-dimensional CBCT (4D CBCT) is valuable for localizing tumors in the lung and liver regions, where the localization accuracy is affected by respiratory motions. However, in image-guided radiation therapy for organs subject to respiratory motion, position verification is often performed using 3D cone beam CT or 2D X-ray images. While it is possible to collimate tumors at specific respiratory phases during breath-holding and to determine the tumor's motion range by taking inspiratory and expiratory breath-hold images, it remains difficult to track the tumor's trajectory at each respiratory phase. The aim of this study is to investigate the positional phases of targets that move with respiration using phantom experiments with 4D CT and 4D CBCT.
To simulate respiratory motion, we captured images of a moving phantom with a simulated tumor synchronized to simulated breathing using 4D CT and 4D CBCT. The simulated tumor was set to have respiratory cycles of 3, 4, 5, and 7.5 s, with displacements 20, 16, 10, 8, and 4 mm per breath. Under these conditions, 4D CT and 4D CBCT images were captured. Using the treatment planning system, regions of interest for the simulated tumors were set from the obtained images of each respiratory phase, identifying the tumor and setting the region as the target. Volume, positional error, and Dice coefficient of the target centroid in the corresponding phase images of 4D CT and 4D CBCT were measured with the treatment planning system.
The positional error of the target centroid between 4D CT and 4D CBCT was generally within ±1 mm. The Dice coefficient for each respiratory phase under each condition of 4D CT and 4D CBCT was generally above 0.8.
It has been suggested that 4D CBCT has the same detection ability as 4D CT for targets with respiratory movement.
锥形束计算机断层扫描（CBCT）是放射治疗中最常用的靶区定位技术。四维CBCT（4D CBCT）对于定位肺部和肝脏区域的肿瘤很有价值，这些部位的定位准确性会受到呼吸运动的影响。然而，在针对受呼吸运动影响的器官进行图像引导放射治疗时，位置验证通常使用三维锥形束CT或二维X射线图像。虽然在屏气期间可以在特定呼吸阶段对肿瘤进行准直，并通过采集吸气和呼气屏气图像来确定肿瘤的运动范围，但要在每个呼吸阶段跟踪肿瘤的轨迹仍然很困难。本研究的目的是通过使用4D CT和4D CBCT的体模实验来研究随呼吸运动的靶区的位置阶段。
为了模拟呼吸运动，我们使用4D CT和4D CBCT对一个带有模拟肿瘤的运动体模进行成像，该模拟肿瘤与模拟呼吸同步。模拟肿瘤的呼吸周期设置为3、4、5和7.5秒，每次呼吸的位移分别为20、16、10、8和4毫米。在这些条件下，采集4D CT和4D CBCT图像。使用治疗计划系统，从每个呼吸阶段获得的图像中设置模拟肿瘤的感兴趣区域，识别肿瘤并将该区域设置为靶区。用治疗计划系统测量4D CT和4D CBCT相应相位图像中靶区质心的体积、位置误差和骰子系数。
4D CT和4D CBCT之间靶区质心的位置误差一般在±1毫米以内。4D CT和4D CBCT每种条件下每个呼吸阶段的骰子系数一般都高于0.8。
有人提出，对于有呼吸运动的靶区，4D CBCT具有与4D CT相同的检测能力。
