AbstractBackgroundAccurate segmentation of lung nodules is of great significance for early screening and diagnosis of lung cancer.PurposeHowever, the heterogeneity of lung nodules and the similarities between them and other lung tissues make it difficult to accurately segment these nodules. As regards the use of deep learning to segment lung nodules, convolutional neural networks would gradually lead to errors accumulating at the network layer due to the presence of multiple upsampling and downsampling layers, resulting in poor segmentation results.MethodsIn this study, we developed a refined segmentation network (RS‐Net) for lung nodule segmentation to solve this problem. Accordingly, the proposed RS‐Net was first used to locate the core region of the lung nodules and to gradually refine the segmentation results of the core region. In addition, to solve the problem of misdetection of small‐sized nodules owing to the imbalance of positive and negative samples, we devised an average dice‐loss function computed on nodule level. By calculating the loss of each nodule sample to measure the overall loss, the network can address the misdetection problem of lung nodules with smaller diameters more efficiently.ResultsOur method was evaluated based on 1055 lung nodules from Lung Image Database Consortium data and a set of 120 lung nodules collected from Shanghai Chest Hospital for additional validation. The segmentation dice coefficients of RS‐Net on these two datasets were 85.90% and 81.13%, respectively. The analysis of the segmentation effect of different properties and sizes of nodules indicates that RS‐Net yields a stable segmentation effect.ConclusionsThe results show that the segmentation strategy based on gradual refinement can considerably improve the segmentation of lung nodules.