PurposeSegmentation of the prostate and surrounding organs at risk from computed tomography is required for radiation therapy treatment planning. We propose an automatic two-step deep learning-based segmentation pipeline that consists of an initial multi-organ segmentation network for organ localization followed by organ-specific fine segmentation.ApproachInitial segmentation of all target organs is performed using a hybrid convolutional-transformer model, axial cross-attention UNet. The output from this model allows for region of interest computation and is used to crop tightly around individual organs for organ-specific fine segmentation. Information from this network is also propagated to the fine segmentation stage through an image enhancement module, highlighting regions of interest in the original image that might be difficult to segment. Organ-specific fine segmentation is performed on these cropped and enhanced images to produce the final output segmentation.ResultsWe apply the proposed approach to segment the prostate, bladder, rectum, seminal vesicles, and femoral heads from male pelvic computed tomography (CT). When tested on a held-out test set of 30 images, our two-step pipeline outperformed other deep learning-based multi-organ segmentation algorithms, achieving average dice similarity coefficient (DSC) of 0.836±0.071 (prostate), 0.947±0.038 (bladder), 0.828±0.057 (rectum), 0.724±0.101 (seminal vesicles), and 0.933±0.020 (femoral heads).ConclusionsOur results demonstrate that a two-step segmentation pipeline with initial multi-organ segmentation and additional fine segmentation can delineate male pelvic CT organs well. The utility of this additional layer of fine segmentation is most noticeable in challenging cases, as our two-step pipeline produces noticeably more accurate and less erroneous results compared to other state-of-the-art methods on such images.
Delineation of the prostate and nearby organs at risk (OARs) is a fundamental step in prostate cancer radiation therapy planning. Such contouring is often done manually, which can be a time-consuming and highly variable process. To alleviate these issues, we propose a fully automated two-step deep learning approach to segment the prostate, bladder, rectum, seminal vesicles, and femoral heads from CT images. The first step localizes the organs of interest using a modified 3D UNet architecture that contains an axial cross-attention module. Final segmentations are then computed for each organ individually using organ-specifically optimized UNet-based models. A total of 275 CT images were used for model training and validation. When evaluated on a hold-out set of 15 image sets, the full pipeline achieved mean dice similarity coefficients (DSC) and 95% Hausdorff distances (95HD, in mm) of 0.8660.034 and 4.461.02 (prostate), 0.9570.014 and 2.910.289 (bladder), 0.8530.044 and 5.101.87 (rectum), 0.7400.117 and 6.729.46 (seminal vesicles), 0.9420.016 and 2.851.04 (left femoral head), 0.9420.018 and 3.041.37 (right femoral head).
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