Multicenter AI- versus expert-assisted RECIST target lesion measurements in follow-up body CT of patients with cancer

Background: Manual lesion measurements remain the standard for assessing oncologic treatment response, despite being time-consuming and prone to substantial interreader variability, which may lead to inconsistent response classification and subsequent variability in treatment decisions. Purpose: To evaluate the impact of an artificial intelligence (AI) system for assisted lesion measurement on reading time and measurement consistency in follow-up CT examinations using the Response Evaluation Criteria in Solid Tumors (RECIST 1.1). Methods and Materials: In this retrospective reader study, follow-up chest-abdomen-pelvis CT examinations from 212 oncology patients collected at 2 Dutch hospitals were assessed by 23 readers (15 radiologists, 8 residents) recruited from 11 international institutions under 3 conditions: unassisted, AI-assisted, and expert-assisted (using a prior radiologist's unassisted measurement). To prevent bias related to the source of the measurements, readers were informed that all support was AI-derived. Primary outcomes were reading time to completion and interobserver measurement variability. For each outcome, a Bayesian generalized linear mixed model was used to analyze the results. Results: AI assistance significantly reduced per-patient reading time versus unassisted reading (-36.0 s; 95% CI, -53.0 to -22.1). At the lesion level, it was associated with a small increase in variability relative to the expert-derived reference standard (1.32 mm; 95% CI, 0.83-1.91). At the patient level, AI assistance did not meaningfully affect change in the sum of longest diameters (-0.38 mm; 95% CI, -1.57 to 0.72), but increased RECIST outcome agreement by 7.7% (95% CI, 2.8-12.7) compared with unassisted reading. Expert-assisted reading yielded even higher interreader agreement (13.3%; 95% CI, 8.6-18.1). Conclusion: AI assistance reduced reading time and improved patient-level RECIST agreement, despite a small increase in lesion-level measurement variability. These findings suggest that AI-assisted RECIST assessment may improve workflow and response classification consistency, while also providing a benchmark from expert-assisted reading for future AI development.