Repeatability of Semi-Quantitative and Volumetric Features from Artificial-Intelligence-Guided Lesion Segmentation on...

Objectives: This study evaluated the test-retest repeatability of semi-quantitative and volumetric features derived from artificial intelligence (AI)-assisted lesion segmentation on ¹⁸F-DCFPyL Prostate Specific Membrane Antigen (PSMA)-PET/CT imaging of patients with prostate cancer (PCa). Specifically, we assessed the reliability of maximum, minimum and total standardized uptake values (SUV_max, SUV_mean, SUV_total) and lesion volume measurements across varying lesion sizes and explored the implications of variability for clinical decision-making. Methods: We analyzed ¹⁸F-DCFPyL PSMA-PET/CT images from 22 patients with metastatic PCa. Lesion segmentation was performed using the AI-guided TRAQinform IQ technology, followed by a manual review to eliminate potential false-positive sites of uptake. Lesion-level test-retest repeatability was evaluated using 95% limits of agreement (LOA), intra-class correlation coefficient (ICC), within-subject coefficient of variation (wCOV) and Bland-Altman analysis for SUV and volumetric parameters. Lesions were stratified by size (>1 cm³ and >1.5 cm³) to assess the impact of lesion volume cut-offs on measurement variability. Results: A total of 297 lesions were analyzed, including 191 lesions > 1 cm³ and 161 lesions > 1.5 cm³. Test-retest variability was higher in smaller lesions, with narrower LOA and lower wCOV for larger lesions. SUV_max and SUV_mean exhibited lower variability than SUV_total and lesion volume. The 95% LOA for SUV_max ranged from -33.81% to +38.02% for all lesions, improving to -31.82% to +31.01% for lesions > 1.5 cm³. Similar trends were observed for SUV_mean, SUV_total, and volume. Bland-Altman plots confirmed reduced variability in larger lesions, with no significant systematic bias. Conclusions: The test-retest repeatability of AI-assisted PSMA-PET/CT features varies by feature type, with semi-quantitative features demonstrating improved repeatability relative to volumetric features. Additionally, repeatability is influenced by lesion size, with larger lesions exhibiting greater reliability. These findings highlight the importance of lesion size-dependent thresholds in response assessment and variability-aware feature selection in prognostic models. Current algorithms may be better optimized for larger lesions and higher volumes of disease, with limitations remaining in the robust detection and segmentation of smaller/more subtle lesions.