Cumulative Ionizing Radiation Exposure in Deceased-Donor Kidney Transplant Recipients

Background: Kidney transplant recipients carry a substantially increased risk of malignancy. Ionizing radiation from medical imaging is a recognized but seldom-quantified contributor to this risk. We aimed to characterize cumulative exposure to ionizing radiation from medical imaging after transplantation in deceased-donor kidney transplant (DDKT) recipients. Methods: This single-center retrospective study included all DDKT recipients transplanted between June 2006 and June 2018 with at least six months of follow-up. All radiologic procedures involving ionizing radiation—direct and contrast radiography, computed tomography (CT), fluoroscopy, coronary angiography, and nuclear medicine—were retrieved from the institutional radiology database. Typical effective doses were assigned from published catalogs using International Commission on Radiological Protection (ICRP) Publication 103 tissue-weighting factors. CT-specific cumulative effective dose (CED) was computed per examination with the ImPACT CT Patient Dose Calculator v1.02 (Monte Carlo-based). Recipients were stratified into low- (0–20 mSv), moderate- (>20–50 mSv), high- (>50–100 mSv), and very-high-dose (>100 mSv) categories. Results: 350 DDKT recipients (mean age 43.9 ± 11.3 years, 43.4% female) were followed for a median of 4.8 years (interquartile range [IQR] 2.71–7.51), yielding 1861 patient-years. A total of 9636 ionizing-radiation procedures were performed; 7600 (78.9%) were plain radiographs, and 875 (9.1%) were CT scans. Mean total CED was 36.0 ± 34.5 mSv (median 24.7, IQR 10.6–50.8 mSv). Median annual CED was 5.32 mSv (IQR 1.68–14.50). CT accounted for 69.4% of the total CED. Twenty-six percent (n = 92) of recipients had a CED above 50 mSv and 6.3% (n = 22) above 100 mSv. Older recipients (above the median age of 45 years) had a significantly higher mean total CED than younger recipients (41.8 ± 36.0 vs 30.3 ± 32.0 mSv; mean difference 11.5 mSv, 95% confidence interval [CI] 4.7–18.3; p = 0.014). In multivariable analysis, delayed graft function was the only factor independently associated with higher CED (CED ratio 1.43, 95% CI 1.05–1.93) and more CT examinations, whereas recipient age was not independently associated with CED after adjustment. Conclusions: A substantial proportion of DDKT recipients are exposed to non-trivial cumulative doses of ionizing radiation after transplantation, primarily driven by CT imaging. These are descriptive exposure data: the study did not assess clinical outcomes and does not demonstrate any clinical harm attributable to imaging-related radiation, and the expected radiation-attributable cancer risk is modest in absolute terms. Therefore, clinically indicated imaging should not be curtailed; rather, care-neutral measures—tracking of cumulative dose, preferential use of non-ionizing modalities where diagnostically equivalent, and low-dose CT protocols—are reasonable, particularly in younger recipients and in those with delayed graft function.