Scientific findings and the profession’s collective knowledge regarding cancer risks from radiation exposure resulting from CT scans are uncertain at best and are not enough to justify a policy requiring informed consent from patients and guardians, according to an editorial published in the May issue of Radiology.
The editorial, coauthored by H. Benjamin Harvey, MD, JD, and James Brink, MD, of Massachusetts General Hospital; and Donald P. Frush, MD, of Duke University Medical Center, argues that updates to influential studies and conflicting study results on the potential risks—and benefits—are reason enough to reject the notion of implementing informed consent policies prior to undergoing imaging procedures. “CT is one of the most important medical discoveries of the 20th century, and its use has resulted in invaluable contributions to disease diagnosis, treatment, and monitoring,” wrote Harvey et al. “In the absence of a proved radiation risk, our current efforts to protect patients could do more harm than good by discouraging clinically indicated diagnostic imaging or encouraging the substitution of suboptimal nonradiation-based imaging modalities.”
The doctors noted recent updates to the oft-cited BEIR VII report, which endorsed a linear no-threshold (LNT) risk model for low-dose radiation (LDR) based on cancer studies of atomic bomb survivors and nuclear plant workers exposed to radiation. “Since the 2006 publication of the BEIR VII report, updated atomic bomb survivor data that include more than 120,000 subjects and 6 years of additional data have been published,” the authors wrote. “Analysis of this more comprehensive data set revealed findings that are qualitatively different than previous data sets with regard to carcinogenesis from LDR.”
Specifically, the nonlinearity of the dose-response curve is now statistically significant at low radiation doses, with an upward curvature observed in a dose range limited to 0-2 Gy. “These findings underscore the problematic nature of using statistically convenient wide dose ranges as evidence of the linearity of LDR,” wrote Harvey et al.
Also at issue is a finding of increased cancer risk associated with low-dose exposure to radiation in a study of nuclear workers that analyzed 154 different nuclear power facilities in 15 different countries. “Upon closer scrutiny, it was found that the statistically significant increase was driven by a single subgroup of workers that comprised 3,088 employees of a single Canadian facility who were hired before 1965,” the authors wrote, adding that in some cases, radiation exposure has been shown to benefit patients. “Experts who believe in radiation hormesis hold that LDR may even protect the body against endogenous carcinogenic processes by inducing radiobiologic effects that may repair naturally occurring DNA damage.”
According to Harvey and his colleagues, all of this adds up to uncertain and often confusing data that in no way justify the need for informed consent. “If we were to impose a requirement of informed consent, the process of consent would be circuitous,” the doctors argue. “To be truthful and not misleading—fundamental principles of informed consent—a practitioner would have to state that there is an unproved possibility that the CT study could increase the risk for cancer and then state that there is an unproved possibility that it may not affect, or may even decrease, the risk for cancer.”
Despite these assertions, radiology safety groups such as ImageWisely continue to caution patients and their doctors about the risks associated with radiation exposure. “The prevailing scientific view is that there is a finite (though small) amount of risk involved with such exposures,” reads the ImageWisely website. “The risk is increased with the amount of exposure, with repeated exposures, and when the patient is young.” But Harvey and his coauthors believe at the very least, substantiated scientific findings are necessary to justify informed consent. “We look forward to the time when a preponderance of quality scientific evidence provides an answer to this important question,” wrote Harvey et al. “Notwithstanding the substantial complexities associated with implementing an informed consent process for CT radiation, we believe that the available scientific evidence alone fails to justify obtaining informed consent for CT.”