Richart José, Carmona-Meseguer Vicente, García-Martínez Teresa, Herreros Antonio, Otal Antonio, Pellejero Santiago, Tornero-López Ana, Pérez-Calatayud José
Hospital Clínica Benidorm, Medical Physics Department, Alicante, Spain.
Hospital La Fe-IRIMED, Department of Radiation Oncology, Medical Physics Section, Valencia, Spain.
Rep Pract Oncol Radiother. 2018 Nov-Dec;23(6):547-561. doi: 10.1016/j.rpor.2018.06.005. Epub 2018 Jul 23.
Brachytherapy plays an essential role in the curative intent management of locally advanced cervical cancer. The introduction of the magnetic resonance (MR) as a preferred image modality and the development of new type of applicators with interstitial components have further improved its benefits. The aim of this work is to review the current status of one important aspect in the cervix cancer brachytherapy procedure, namely catheter reconstruction. MR compatible intracavitary and interstitial applicators are described. Considerations about the use of MR imaging (MRI) regarding appropriate strategies for applicator reconstruction, technical requirements, MR sequences, patient preparation and applicator commissioning are included. It is recommendable to perform the reconstruction process in the same image study employed by the physician for contouring, that is, T2 weighted (T2W) sequences. Nevertheless, a clear identification of the source path inside the catheters and the applicators is a challenge when using exclusively T2W sequences. For the intracavitary component of the implant, sometimes the catheters may be filled with some substance that produces a high intensity signal on MRI. However, this strategy is not feasible for plastic tubes or titanium needles, which, moreover, induce magnetic susceptibility artifacts. In these situations, the use of applicator libraries available in the treatment planning system (TPS) is useful, since they not only include accurate geometrical models of the intracavitary applicators, but also recent developments have made possible the implementation of the interstitial component. Another strategy to improve the reconstruction process is based on the incorporation of MR markers, such as small pellets, to be used as anchor points. Many institutions employ computed tomography (CT) as a supporting image modality. The registration of CT and MR image sets should be carefully performed, and its uncertainty previously assessed. Besides, an important research work is being carried out regarding the use of ultrasound and electromagnetic tracking technologies.
近距离放射治疗在局部晚期宫颈癌的根治性治疗中起着至关重要的作用。磁共振（MR）作为首选成像方式的引入以及新型带间质组件的施源器的开发进一步提高了其疗效。这项工作的目的是回顾宫颈癌近距离放射治疗过程中一个重要方面的现状，即导管重建。描述了与MR兼容的腔内和间质施源器。包括了关于使用MR成像（MRI）进行施源器重建的适当策略、技术要求、MR序列、患者准备和施源器调试的考虑因素。建议在医生用于勾画轮廓的同一图像研究中进行重建过程，即T2加权（T2W）序列。然而，仅使用T2W序列时，清晰识别导管和施源器内的源路径是一项挑战。对于植入物的腔内组件，有时导管可能填充有在MRI上产生高强度信号的物质。然而，这种策略对于塑料管或钛针不可行，而且它们会引起磁敏感性伪影。在这些情况下，使用治疗计划系统（TPS）中可用的施源器库很有用，因为它们不仅包括腔内施源器的精确几何模型，而且最近的发展使得间质组件的实施成为可能。另一种改进重建过程的策略是基于纳入MR标记物，如小颗粒，用作锚点。许多机构使用计算机断层扫描（CT）作为辅助成像方式。CT和MR图像集的配准应仔细进行，并预先评估其不确定性。此外，关于超声和电磁跟踪技术的使用正在开展重要的研究工作。
