Biological dosimetry for iodine contrast medium and X-ray interactions by cell survival

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Abstract
In the presence of an iodinated contrast medium, X-ray absorption is enhanced owing to photoelectric interactions. This has been shown both experimentally and in patients undergoing radiographic procedures using contrast media (Adams et al, 1977; Norman et al, 1978; Callisen et al, 1979; Cockran et al, 1980; Matsudaira et al, 1980; Matsubara et al, 1982). Chromosome aberration assays of circulating lymphocytes in these patients revealed a significant increase in absorbed dose compared with those who underwent a similar radiological procedure without the use of contrast media. This effect is most significant at X-ray energy levels just above the binding energy of iodine K electrons. Ejected photoelectrons are estimated to deposit their energy within a few micrometers in tissue (Cole, 1969). In angiography, an iodine contrast medium is irradiated in small blood vessels so that attenuation and “hardening” of X rays are unlikely to be significant. However, when a larger volume of tissue is irradiated in the presence of a contrast medium, the X rays become not only attenuated but also “hardened” as they travel through the iodine-containing tissue. In contrast to the incident X rays, the exit X rays are predicted to be less effective in eliciting photoelectric interactions because of the reduction in the “soft” component of the X-ray spectrum. In this communication we report measurements of the dose enhancement as a function of iodine concentration and the effect of X-ray hardening on the photoactivation using biological dosimetry based on cell survival.