Assessing an Automated Noncontrast CT-based Pipeline for Sacral Tumor Classification Using a Hip Bone Reference Frame

Purpose To develop a fully automated hybrid approach to predict sacral tumor types from preoperative noncontrast CT (NCCT ) images. Materials and Methods In this retrospective, multicenter study, scans were available in 690 patients who had histopathologically confirmed preoperative sacral NCCT performed between January 2011 and May 2024. A fully automated hybrid model integrated two deep convolutional neural network models (model 1 and model 2) through a fully automated pipeline. Model 1 segments tumors and hip bones automatically from NCCT images, producing masks that are used by model 2. For the first time, the hip bone was used as a reference frame for tumor localization. The second model, CL-MedImageNet, is an innovative six-classification model that allows the simultaneous input of tumor images, clinical data, and location information. This streamlined, automated system ensures efficient data integration and processing between the two models. The efficacy of the model was assessed in comparison to that of radiologists, using metrics including the area under the curve (AUC), F1 score, and confusion matrix. Results In all, 690 patients (mean age, 46 years ± 17 [SD]; 377 male patients) were included. Segmentation achieved mean Dice coefficients of 0.82 ± 0.11 (validation), 0.81 ± 0.12 (internal test), and 0.81 ± 0.12 (external test) after postprocessing; interobserver Dice coefficient was 0.96. The CL-MedImageNet classifier attained macro average AUCs of 0.89 (95% CI: 0.83, 0.93), 0.88 (95% CI: 0.84, 0.92), and 0.87 (95% CI: 0.79, 0.92) in validation, internal, and external test sets, respectively, with macro average F1 scores of 0.63, 0.63, and 0.56. The highest achieved precision and sensitivity were both 0.66 across all sets. CL-MedImageNet outperformed radiologists (macro average AUCs, 0.87 vs 0.80, P = .002; 0.87 vs 0.83, P = .45). Conclusion The fully automated NCCT-based CL-MedImageNet pipeline demonstrated high segmentation accuracy and robust six-class classification, outperforming expert radiologists. Keywords: Applications - CT, Deep Learning, Radiomics, Segmentation, Skeletal-Axial, Pelvis, Sacral Tumors Supplemental material is available for this article. © The Author(s) 2026. Published by the Radiological Society of North America under a CC BY 4.0 license.