Division of Medical Physics and Engineering, Graduate School of Medicine, Hokkaido University, Sapporo, Japan.
Phys Med Biol. 2011 Aug 7;56(15):4803-13. doi: 10.1088/0031-9155/56/15/011. Epub 2011 Jul 13.
In the real-time tumor-tracking radiotherapy system, fluoroscopy is used to determine the real-time position of internal fiducial markers. The pattern recognition score (PRS) ranging from 0 to 100 is computed by a template pattern matching technique in order to determine the marker position on the fluoroscopic image. The PRS depends on the quality of the fluoroscopic image. However, the fluoroscopy parameters such as tube voltage, current and exposure duration are selected manually and empirically in the clinical situation. This may result in an unnecessary imaging dose from the fluoroscopy or loss of the marker because of too much or insufficient x-ray exposure. In this study, a novel optimization method is proposed in order to minimize the fluoroscopic dose while keeping the image quality usable for marker tracking. The PRS can be predicted in a region where the marker appears to move in the fluoroscopic image by the proposed method. The predicted PRS can be utilized to judge whether the marker can be tracked with accuracy. In this paper, experiments were performed to show the feasibility of the PRS prediction method under various conditions. The predicted PRS showed good agreement with the measured PRS. The root mean square error between the predicted PRS and the measured PRS was within 1.44. An experiment using a motion controller and an anthropomorphic chest phantom was also performed in order to imitate a clinical fluoroscopy situation. The result shows that the proposed prediction method is expected to be applicable in a real clinical situation.
在实时肿瘤跟踪放射治疗系统中，透视用于确定内部基准标记物的实时位置。通过模板模式匹配技术计算模式识别得分（PRS），范围从 0 到 100，以确定透视图像上的标记位置。PRS 取决于透视图像的质量。然而，在临床情况下，透视参数（如管电压、电流和曝光时间）是手动和经验性选择的。这可能导致透视产生不必要的成像剂量，或者由于 X 射线曝光过多或不足而丢失标记。在这项研究中，提出了一种新的优化方法，以便在保持图像质量可用于标记跟踪的同时，最小化透视剂量。通过所提出的方法，可以预测标记物在透视图像中移动的区域中的 PRS。可以利用预测的 PRS 来判断标记物是否可以准确跟踪。本文进行了实验，以展示在各种条件下 PRS 预测方法的可行性。预测的 PRS 与测量的 PRS 吻合良好。预测的 PRS 与测量的 PRS 之间的均方根误差在 1.44 以内。还进行了使用运动控制器和拟人胸部体模的实验，以模拟临床透视情况。结果表明，所提出的预测方法有望在实际临床情况下应用。
