Recurrent CT imaging and strategies for patient radiation protection

Computed tomography (CT) contributes disproportionately to medical radiation exposure. While most patients undergo only a few examinations, a subset accumulates high cumulative effective doses (CEDs), raising concern for long-term stochastic risks. Recently, the concept of a recurrent exposure reference level (RERL) has been proposed as a benchmark for cumulative dose monitoring in recurrently imaged patients. To evaluate cumulative radiation exposure from recurrent CT imaging in a tertiary care hospital, determine the proportion of patients exceeding high-dose thresholds, and establish a local RERL. All adult CT examinations performed at Vilnius University Hospital Santaros Klinikos between 2022 and 2024 were retrospectively analysed. Recurrent patients were defined as those with at least one CT in 2023 and an additional CT in 2022, 2023, or 2024. Outcome measures included the annual and three-year incidence and prevalence of CED ⩾ 100 mSv, dose distributions, and RERL determination as the 75th percentile of annual CED among recurrent patients. Over three years, 78 258 patients underwent 99 865 CT examinations. The annual number of patients and exams increased steadily, but the yearly incidence of high-dose patients (CED ⩾ 100 mSv) remained stable at ∼2%. Across the full cohort, 1633 patients (3.6%) exceeded 100 mSv, and 29 patients (0.04%) surpassed 500 mSv. Among 9199 recurrent patients (35.6% of the total), 18.2% exceeded 100 mSv within three years. Most patients (68%) crossed this threshold with fewer than five CTs. The local RERL, defined as the 75th percentile of annual CED in recurrent patients, was 36 mSv. A subset of patients in a tertiary care setting accumulated high radiation doses from recurrent CT, often with relatively few examinations. The derived RERL aligns closely with values reported in other European studies, supporting its use as a practical benchmark for monitoring cumulative dose. Systematic dose tracking, integration of RERLs, and strict adherence to justification and optimisation are essential to mitigate risks while preserving the diagnostic value of CT.