*Result*: Pediatric Personalized Deep Learning Models for Segmentation of Hepatoblastoma at CT and MRI.
*Further Information*
*Purpose To evaluate the generalizability of adult-trained models for hepatoblastoma segmentation to pediatric patients and to develop two deep learning (DL) models, INLINEMATH and INLINEMATH , specifically trained on pediatric contrast-enhanced CT and T2-weighted MRI scans, respectively. Materials and Methods Imaging data from the multicenter Children's Oncology Group AHEP0731 trial (NCT00980460; May 2008-July 2018) were analyzed. DL models employing the three-dimensional U-Net architecture were trained using D<subscript>CT-Train</subscript> and D<subscript>MRI-Train</subscript>. These models were evaluated on D<subscript>CT-Val</subscript> and D<subscript>MRI-Val</subscript> using the Dice similarity coefficient (DSC), and model segmentations were compared with manual segmentations from three annotators (R<subscript>1</subscript>, R<subscript>2</subscript>, and R<subscript>3</subscript>), their consensus (R<subscript>c</subscript>), and adult-trained model ( INLINEMATH ) segmentations. Volume percentage error analysis was performed to evaluate segmentation precision. Results A total of 104 participants (mean age ± SD, 28.2 months ± 30.5; 64 male; D<subscript>CT-Train</subscript> = 56, D<subscript>CT-Val</subscript> = 48) were included in the CT dataset and 123 (31.5 months ± 38.4; 87 male; D<subscript>MRI-Train</subscript> = 50, D<subscript>MRI-Val</subscript> = 73) in the MRI dataset. INLINEMATH achieved good agreement with consensus segmentation (DSC = 0.86 [95% CI: 0.80, 0.91]) and exhibited higher agreement than INLINEMATH with R<subscript>1</subscript> (0.83 vs 0.55), R<subscript>2</subscript> (0.85 vs 0.55), R<subscript>3</subscript> (0.84 vs 0.54), and R<subscript>c</subscript> (0.86 vs 0.55) segmentations. Volume percentage error analysis revealed that INLINEMATH achieved segmentation results on par with or better than those of a novice annotator (R<subscript>3</subscript>) in high-precision scenarios. INLINEMATH also achieved a DSC of 0.86, demonstrating good agreement with R<subscript>c</subscript>. Conclusion The pediatric-trained DL-based models outperformed adult-trained models for accurate segmentation of pediatric hepatoblastoma. Keywords: Pediatrics, Deep Learning, Liver, MR-Imaging, Abdomen/GI, Algorithm Development ClinicalTrials.gov NCT00980460 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.*