Frequencies of micronucleated reticulocytes, a dosimeter of DNA double-strand breaks, in infants receiving computed tomography or cardiac catheterization.

The use of computed tomography (CT scans) has increased dramatically in recent decades, raising questions about the long-term safety of CT-emitted x-rays especially in infants who are more sensitive to radiation-induced effects. Cancer risk estimates for CT scans typically are extrapolated from models; therefore, new approaches measuring actual DNA damage are needed for improved estimations. Hence, changes in a dosimeter of DNA double-strand breaks, micronucleated reticulocytes (MN-RETs) measured by flow cytometry, were investigated in mice and infants exposed to CT scans. In male C57BL/6N mice (6-8 weeks-of-age), there was a dose-related increase in MN-RETs in blood samples collected 48h after CT scans delivering targeted exposures of 1-130 cGy x-rays (n=5-10/group, r=0.994, p=0.01), with significant increases occurring at exposure levels as low as 0.83 cGy x-rays compared to control mice (p=0.002). In paired blood specimens from infants with no history of a prior CT scan, there was no difference in MN-RET frequencies found 2h before (mean, 0.10±0.07%) versus 48h after (mean, 0.11±0.05%) a scheduled CT scan/cardiac catheterization. However, in infants having prior CT scan(s), MN-RET frequencies measured at 48h after a scheduled CT scan (mean=0.22±0.12%) were significantly higher than paired baseline values (mean, 0.17±0.07%; p=0.032). Increases in baseline (r=0.722, p<0.001) and 48-h post exposure (r=0.682, p<0.001) levels of MN-RETs in infants with a history of prior CT scans were significantly correlated with the number of previous CT scans. These preliminary findings suggest that prior CT scans increase the cellular responses to subsequent CT exposures. Thus, further investigation is needed to characterize the potential cancer risk from single versus repeated CT scans or cardiac catheterizations in infants.