The standard treatment for the cancer is the radiotherapy where the organs nearby the target volumes get affected during treatment called the Organs-at-risk. Segmentation of Organs-at-risk is crucial but important for the proper planning of radiotherapy treatment. Manual segmentation is time consuming and tedious in regular practices and results may vary from experts to experts. The automatic segmentation will produce robust results with precise accuracy. The aim of this systematic review is to study various techniques for the automatic segmentation of organs-at-risk in thoracic computed tomography images and to discuss the best technique which give the higher accuracy in terms of segmentation among all other techniques proposed in the literature. PRISMA guidelines had been used to conduct this systematic review. Three online databases had been used for the identification of the related papers and a query had been formed for the search purpose. The papers were shortlisted based on the various inclusion and exclusion criteria. Four research questions had been designed and answers of those were explored. After reviewing all the techniques, the best technique had been selected and discussed in detail which gave the precise accuracy based on Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD). Both DSC and HD were used in the literature to evaluate the performance of their proposed technique for the automatic segmentation of four organs (esophagus, heart, trachea and aorta). However, the value of these parameters vary as per the validation sample size. Consequently, various challenges faced by the researchers had been listed. This paper includes the summary of the various automatic segmentation techniques for the Organs-at-risk in thoracic computed tomography images in terms of four research questions. Different techniques, Datasets, Performance accuracy and various challenges had been discussed.

癌症的标准治疗方法是放射疗法，在这种治疗方法中，目标体积附近的器官会在被称为“危险器官”的治疗过程中受到影响。危险器官的分割至关重要，但对于正确规划放疗治疗也很重要。手动分段在常规操作中既费时又乏味，结果可能因专家而异。自动分割将产生准确准确的鲁棒结果。本系统综述的目的是研究各种在胸部计算机断层扫描图像中对器官进行自动分割的技术，并讨论在文献中提出的所有其他技术中分割精度更高的最佳技术。PRISMA指南已用于进行系统的审查。三个在线数据库已用于识别相关论文，并已形成查询以进行搜索。论文根据各种纳入和排除标准入围。设计了四个研究问题，并探讨了这些问题的答案。在回顾了所有技术之后，我们选择并详细讨论了最佳技术，该技术基于骰子相似度系数（DSC）和Hausdorff距离（HD）提供了精确的精度。文献中使用DSC和HD来评估其提议的技术对四个器官（食道，心脏，气管和主动脉）自动分割的性能。但是，这些参数的值根据验证样本大小而有所不同。因此，列出了研究人员面临的各种挑战。本文从四个研究问题的角度总结了胸腔计算机断层扫描图像中处于危险中的器官的各种自动分割技术。讨论了不同的技术，数据集，性能准确性和各种挑战。