IEEE Trans Med Imaging. 2019 Feb;38(2):406-416. doi: 10.1109/TMI.2018.2865547. Epub 2018 Aug 16.
External beam radiotherapy is extensively used to treat cervical carcinomas. A single planning CT scan enables the calculation of the dose distribution. The treatment is delivered over five weeks. Large per-treatment anatomical variations may hamper the dose delivery, with the potential of an organ-at-risk (OAR) overdose and a tumor underdose. To anticipate these deformations, a recent approach proposed three planning CTs with variable bladder volumes, which had the limitation of not covering all per-treatment anatomical variations. An original patient-specific population-based library has been proposed. It consisted of generating two representative anatomies, in addition to the standard planning CT anatomy. First, the cervix and bladder meshes of a population of 20 patients (314 images) were registered to an anatomical template, using a deformable mesh registration. An iterative point-matching algorithm was developed based on local shape context (histogram of polar or cylindrical coordinates and geodesic distance to the base) and on a topology constraint filter. Second, a standard principal component analysis (PCA) model of the cervix and bladder was generated to extract the dominant deformation modes. Finally, specific deformations were obtained using posterior PCA models, with a constraint representing the top of the uterus deformation. For a new patient, the cervix-uterus and bladder were registered to the template, and the patient's modeled planning library was built according to the model deformations. This method was applied following a leave-one-patient-out cross-validation. The performances of the modeled library were compared to those of the three-CT-based library, showing an improvement in both target coverage and OAR sparing.
外照射放疗广泛用于治疗宫颈癌。单次计划 CT 扫描可计算剂量分布。治疗分五周进行。每次治疗时的解剖结构的较大变化可能会阻碍剂量输送，从而导致危及器官（OAR）超量和肿瘤剂量不足。为了预测这些变形，最近提出了三种具有可变膀胱体积的计划 CT，但其局限性在于不能涵盖所有每次治疗的解剖变化。已经提出了一种原始的基于患者特定的基于人群的库。它包括生成两个代表性解剖结构，除了标准计划 CT 解剖结构之外。首先，使用可变形网格配准，将 20 名患者（314 张图像）的子宫颈和膀胱网格配准到解剖模板。基于局部形状上下文（极坐标或圆柱坐标的直方图和与基础的测地距离）和拓扑约束滤波器开发了迭代点匹配算法。其次，生成了子宫颈和膀胱的标准主成分分析（PCA）模型，以提取主要变形模式。最后，使用后验 PCA 模型获得特定变形，并使用表示子宫顶部变形的约束。对于新患者，将子宫颈-子宫和膀胱配准到模板，并根据模型变形构建患者的模型化计划库。该方法通过离开一位患者的交叉验证进行应用。比较了模型化库的性能与基于三 CT 的库的性能，在目标覆盖和 OAR 保护方面均有所改善。
