Objective: Ensuring the precision in motion tracking for MRI-guided Radiotherapy (MRIgRT) is crucial for the delivery of effective treatments. This study refined the motion tracking accuracy in MRIgRT through the innovation of an automatic real-time tracking method, leveraging an enhanced Tracking-Learning-Detection (ETLD) framework coupled with automatic segmentation. Methods: We developed a novel MRIgRT motion tracking method by integrating two primary methods: the ETLD framework and an improved Chan-Vese model (ICV), named ETLD+ICV. The TLD framework was upgraded to suit real-time cine MRI, including advanced image preprocessing, no-reference image quality assessment, an enhanced median-flow tracker, and a refined detector with dynamic search region adjustments. Additionally, ICV was combined for precise coverage of the target volume, which refined the segmented region frame by frame using tracking results, with key parameters optimized. Tested on 3.5D MRI scans from 10 patients with liver metastases, our method ensures precise tracking and accurate segmentation vital for MRIgRT. Results: An evaluation of 106,000 frames across 77 treatment fractions revealed sub-millimeter tracking errors of less than 0.8mm, with over 99% precision and 98% recall for all subjects, underscoring the robustness and efficacy of the ETLD. Moreover, the ETLD+ICV yielded a dice global score of more than 82% for all subjects, demonstrating the proposed method's extensibility and precise target volume coverage. Conclusions: This study successfully developed an automatic real-time motion tracking method for MRIgRT that markedly surpasses current methods. The novel method not only delivers exceptional precision in tracking and segmentation but also demonstrates enhanced adaptability to clinical demands, positioning it as an indispensable asset in the quest to augment the efficacy of radiotherapy treatments.

本研究针对磁共振成像引导放射治疗中的运动跟踪精度问题进行了改进，提出了一种结合增强跟踪-学习-检测框架与改进的Chan-Vese模型的自动实时运动跟踪方法。测试结果表明，该方法在运动跟踪和分割的精确性上显著优于现有技术，具有极高的适应性，对提高放射治疗的效果具有潜在的重大影响。

A Novel Automatic Real-time Motion Tracking Method for Magnetic
  Resonance Imaging-guided Radiotherapy: Leveraging the Enhanced
  Tracking-Learning-Detection Framework with Automatic Segmentation

用于磁共振成像引导放射治疗的新型自动实时运动跟踪方法：利用增强的跟踪-学习-检测框架与自动分割