A new benchmark shows promise for monitoring cumulative radiation dose in patients who undergo recurrent CT imaging, researchers have reported.
The findings address the need for systematic dose tracking and more rigorous justification of imaging, particularly for frequently scanned patients, according to a team led by Antonio Jreije, MD, of Vilnius University Hospital Santaros Klinikos in Lithuania. The study results were published February 12 in the Journal of Radiological Protection.
“Recently, the concept of a Recurrent Exposure Reference Level (RERL) has been proposed as a benchmark for cumulative dose monitoring in recurrently imaged patients,” the group explained, noting that “the derived RERL aligns closely with values reported in other European studies, supporting its use as a practical benchmark for monitoring cumulative dose.”
CT contributes disproportionately to medical radiation exposure, Jreije and colleagues wrote, and although “most patients undergo only a few examinations [during their lifetimes], a subset accumulates high cumulative effective doses, raising concern for long-term stochastic risks.” The team evaluated cumulative radiation exposure from recurrent CT imaging in a tertiary care hospital to assess the proportion of patients exceeding high-dose thresholds and establish a tailored RERL.
The study included 78,258 patients who underwent 99,865 CT exams between 2022 and 2024. The team defined recurrent patients as those with at least one CT exam in 2023 and an additional exam in 2022, 2023, or 2024. It tracked outcome measures such as annual and three-year incidence and prevalence of cumulative effective doses equal to or greater than 100 mSv, dose distributions, and RERL determination as the 75th percentile of annual cumulative effective dose among patients undergoing repeat CT imaging.
The group reported the following:
- The annual number of patients and exams increased steadily over the study time frame, but the yearly incidence of high-dose patients (cumulative effective dose ≥ 100 mSv) remained stable at roughly 2%.
- Across the full cohort, 1,633 patients (3.6%) exceeded 100 mSv, and 29 patients (0.04%) surpassed 500 mSv.
- Among 9,199 patients who underwent recurrent CT imaging (35.6% of the total), 18.2% exceeded 100 mSv within three years, and most of these (68%) crossed this threshold with fewer than five CT exams (96% crossed the threshold with fewer than 10 scans).
- The local RERL, defined as the 75th percentile of annual cumulative effective dose in recurrent patients, was 36 mSv.
The investigators also found that cancer‑related imaging was the leading cause of high cumulative dose, representing 38% of cases among patients who exceeded 200 mSv. But pancreatitis, pulmonary embolism, bowel pathology, and polytrauma also contributed to elevated exposure: For example, pancreatitis patients accumulated a median cumulative effective dose of 432 mSv, among the highest in the study.
The authors stressed that exceeding the RERL should be considered a prompt to reassess justification for CT imaging and to consider alternative modalities such as MRI or ultrasound.
“Systematic monitoring of cumulative doses, particularly in younger and middle-aged adults with recurrent imaging needs, should become an integral component of radiology practice,” they concluded.
Access the full study here.