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Over the past several years, the cancer risks associated with radiation from diagnostic imaging have received increased attention in both the medical literature and the lay press. In the midst of this heightened scrutiny, there has been growing support for the idea of tracking cumulative dose estimates that longitudinally document the accumulated medical radiation exposure of each individual patient. The authors review the current consensus model of radiation-induced carcinogenesis and use this framework to provide a rational assessment of several potential cumulative dose estimate utilization strategies., (Copyright © 2012 American College of Radiology. Published by Elsevier Inc. All rights reserved.)

Sister-chromatid exchange (SCE) analyses were conducted in maternal, embryonic and extraembryonic tissues of pregnant rats and mice. The various tissues were substituted in vivo with 5-bromodeoxyuridine (BrdU) by implantation of a BrdU tablet in pregnant animals at mid-gestation. Following maternal exposure to 5-20 mg/kg cyclophosphamide, embryonic liver cells demonstrated dose-dependent SCE increases up to 10-fold that of control. Rat embryos revealed little intralitter variability for this transplacental effect. Maternal marrow and yolk sac cells examined in the rat also underwent significant increases in SCE, although to different extents. While marrow SCE frequencies were similar to those of embryo liver, yolk sac SCE frequencies were generally much lower. SCE analyses were also conducted in rat yolk sac cells substituted in vivo with BrdU and subsequently explanted to whole-embryo culture. In vitro exposure to cyclophosphamide at concentrations up to 100 microgram/ml had no SCE-inducing effect. However, similar exposures to phosphoramide mustard, a presumed metabolite of cyclophosphamide, caused dose-dependent increases in SCE up to 8-fold higher than control at 2 microgram/ml. Thus, cyclophosphamide appears to require maternal metabolic activation in order to cause an increased SCE frequency in yolk sac cells. The system described permits versatile SCE analyses which can help to define relative maternal and embryo tissue-specific sensitivities to chemical-induced genetic damage.