Characterizing cumulative lens dose in recurrent CT: A Large-Scale Single-Center cohort study of drivers.

OBJECTIVES: To quantify the distribution and evolution patterns of the annual cumulative lens dose (ACLD) in recurrent CT examinations and identify the key drivers of extreme radiation burdens. MATERIALS AND METHODS: This retrospective cohort study included 118,126 patients who underwent recurrent CT examinations (≥ 2 scans within a 12-month rolling window) at a single center between January 2021 and December 2025. A log-transformed ordinary least squares (OLS) regression model with interaction terms was employed to evaluate ACLD trends. Furthermore, specific attribution analyses were conducted across high-ACLD subgroups-stratified by clinical thresholds of ≥ 100, ≥250, and ≥ 500 mGy-to evaluate the impact of scan frequency, anatomical site, scan type, and clinical indications on extreme dose accumulation. RESULTS: In the total recurrent cohort, the observed median ACLD was 60.637 mGy (IQR: 0.55-105.51 mGy). In the multivariable interaction model, the predicted conditional geometric mean ACLD for the reference profile (a 52-year-old male undergoing non-contrast head CT for neurological indications) was 68.975 mGy. Across the overall cohort, ACLD accumulation demonstrated "scatter-driven proportional growth," with distal sites (chest, abdomen, extremities) showing significantly higher effective geometric mean ratios (GMRs > 1.6) per additional scan. Conversely, in the high-dose subgroups (≥ 250 mGy), the marginal contribution of trunk scatter saturated (GMRs ≈1.0). At extreme dose levels (≥ 500 mGy), ACLD accumulation was overwhelmingly driven by direct head exposures for neurological emergencies, completely neutralizing the influence of baseline physiological characteristics like sex. CONCLUSION: Cumulative lens dose growth evolves dynamically from scatter-driven proportional increases at low baselines to direct exposure-dominated absolute accumulation at high burdens. Implementing organ-specific dose monitoring is crucial for high-frequency imaging patients.