Development of the real-time four-dimensional cone beam CT reconstruction technique for interactive radiotherapy

我们提出了一种基于实时肿瘤跟踪技术的四维锥形束计算机断层扫描（CBCT）重建新方法。在实时肿瘤跟踪中，在正交透视图像中检测肿瘤附近插入的基准标记物。标记的三维位置每33毫秒计算一次，精度为1毫米。根据标记的位置，投影图像可以分为几个阶段。因此，在每个阶段都可以进行四维CBCT重建。利用与北海道大学医院质子治疗系统成像设备相同的试验机，通过经验评估4D CBCT重建的可行性。此外，我们还分析了肿瘤运动基线偏移的特征，以探讨4D CBCT重建方法的有效性。通过研究，证实了4D CBCT重建的可行性和有效性。

We have proposed a novel method for four-dimensional (4D) cone-beam computed tomography (CBCT) reconstruction with real-time tumor tracking technique. In the real-time tumor tracking, a fiducial marker inserted near the tumor is detected in the orthogonal fluoroscopic images. The three-dimensional position of the marker is calculated every 33 msec with an accuracy of 1 mm. According to the position of the marker, projection images can be classified into some phases. Four dimensional CBCT reconstruction is therefore available in each phase. Feasibility of the 4D CBCT reconstruction was evaluated through the experience using the testing machine, which has the same imaging devices in the proton therapy system in Hokkaido University Hospital. Additionally, characteristics of intrafractional baseline shift of tumor motion were analyzed to investigate efficacy of the 4D CBCT reconstruction method. Through the study, the feasibility and efficacy of the 4D CBCT reconstruction was confirmed.