Bone Metastasis Detection at CT with Deep Learning Models Trained Using Multicenter, Multimodal Reference Standards: Development and Evaluation.

Purpose To develop and validate deep learning models for detecting bone metastases on abdominal and thoracic CT scans, considering lesion visibility, and to compare model performance against human readers. Materials and Methods This retrospective multicenter study included CT scans in patients with bone metastases at four medical centers (August 2013-October 2021). MRI and PET/CT served as reference standards to categorize lesions as visible, indeterminate, or invisible based on CT visibility. Two nnU-Net models were trained: model 1 with only CT-visible metastases and model 2 with both visible and indeterminate metastases. Lesion-level performance was evaluated using precision and recall. Scan-level performance was evaluated using area under the receiver operating characteristic curve. Model performance was compared with that of three musculoskeletal radiologists and three radiologists in training. Results A total of 502 CT scans in 332 patients (mean age ± SD, 64.2 years ± 11.2; 171 male) with 4999 bone metastases were included. Although lesion-level precision was similar between both models (model 2: 80.1%; model 1: 78.8%; P = .41), model 2 achieved higher recall overall (41.8% vs 33.9%; P < .001) and among visible lesions (53.6% vs 44.7%; P < .001). Both models' precision exceeded that of radiologists in training (66.6%; P < .003) and musculoskeletal radiologists (66.5%; P < .004). Only model 2 achieved recall comparable with that of both radiologists in training (39.4%; P = .37) and musculoskeletal radiologists (43.8%; P = .47), as well as a comparable scan-level area under the receiver operating characteristic curve (0.80 [95% CI: 0.67, 0.90]; P > .05). Conclusion The deep learning model trained with multimodal reference standards achieved expert-level bone metastasis detection performance at body CT. Keywords: CT, Abdomen/GI, Skeletal/Axial, Skeletal-Appendicular, Thorax, Metastases, Technology Assessment, Comparative Studies, Segmentation, Supervised Learning, Convolutional Neural Network (CNN), Bone Metastasis, Body CT, Deep Learning, Multimodal Reference Standards Supplemental material is available for this article. © RSNA, 2026 See also commentary by Khosravi in this issue.