SegTHOR, short for Segmentation of THoracic Organs at Risk, is an image dataset for segmenting thoracic organs at risk (OARs, thoracic organs at risk, are organs that must be preserved around the tumor during radiotherapy). In this dataset, OARs are the heart, trachea, aorta, and esophagus, which have different shapes and appearance characteristics. The dataset includes 60 3D CT scan images, 40 for training and 20 for testing, and the OARs in the images are manually annotated by experienced radiotherapists.