Establishment of recurrent exposures reference levels for repeated computed tomography examinations in adult patients on a nationwide level in Slovakia

Introduction: The study aims were: (1) to assess the incidence in 1 year, the cumulative incidences and the period prevalence in 3/5 years of the condition of patients accruing cumulative effective dose (CED) ≥ 100 mSv in health care centres providing CT examinations in Slovakia; and (2) to quantify their variability among different centres, to test the feasibility of establishing recurrent exposure reference levels (RERL) on a nationwide level.

Materials and methods: The data were tracked during five consecutive years using the CT dose index and dose-length-product along with the patient's ID. ED was calculated using conversion factors. Hospitals were stratified according to the number of beds in clinics (0), small (< 200), medium (201-500), or large (> 500) hospitals.

Results: The database included 1,278,928 patients who underwent 2,157,508 CT exams in 5 years. The I_100;1 (%), I_100;3 (%), I_100;5 (%) ranged from 0% to 6.2%, from 0.3% to 23.2% and from 0.3% to 36.9%, respectively. The P_100;3 (%), P_100;5 (%) ranged from 0.17% to 13.3% and from 0.19% to 17.8%, respectively. No significant differences were found in epidemiological indexes among different hospital sizes. A strong positive correlation was found between the third quartile values of yearly CED and I_100;1 (%) (r = 0.84; R² = 0.70; p < 0.0001). RERL value, set as the 75th percentiles of the distributions of the 3rd quartiles of the yearly CED, amounted to 25.7 mSv.

Conclusion: The management of patients with recurrent CT exposures is highly variable among hospitals and unrelated to the size of the institution. Incidence should be reported instead of prevalence.

Key points: Question Beyond just reporting statistics on recurrent imaging, the question which needs to be addressed is how to use such information to optimise patient protection. Findings In Slovakia the 5-year incidence of patients with CED ≥ 100 mSv average 6% and range from 0.3% to 36.9% among different hospitals. Clinical relevance The incidence of patients with CED ≥ 100 mSv is highly variable among hospitals and unrelated to their size. The heterogeneity in the radiation exposure of recurrent patients prompts the introduction of RERL to aid in the optimisation of patient protection.