Imaging Studies

From Heartwire

“Worrisome” Radiation Doses With Imaging, New Study Finds Michael O’Riordan

August 27, 2009 (Atlanta, Georgia) — Medical imaging procedures expose many nonelderly clients to substantial doses of ionizing radiation, according to the results of a new study [1]. Myocardial perfusion imaging alone accounts for 22% of the radiation dose from all study procedures, while computed-tomography (CT) scans of the abdomen, pelvis, and chest account for nearly 38%, report investigators.

“Our findings that in some clients worrisome radiation doses from imaging procedures can accumulate over time underscores the need to improve their use,” write lead investigator Dr Reza Fazel (Emory University School of Medicine, Atlanta, GA) and colleagues. “Unlike the exposure of workers in healthcare and the nuclear industry, which can be regulated, the exposure of clients cannot be restricted, largely because of the inherent difficulty in balancing the immediate clinical need for these procedures, which is frequently substantial, against the stochastic risks of cancer that would not be evident for years, if at all.”

The analysis, which studied 952 420 adults aged 18 to 64 years in five US cities, is published in the August 27, 2009 issue of the New England Journal of Medicine.

During the study period, which ran from 2005 to 2007, 655 613 adults underwent at least one imaging procedure associated with radiation exposure. The mean effective dose was 2.4 mSv per person per year, although a wide distribution was noted. Moreover, the proportion of subjects undergoing procedures and their mean doses varied according to age, sex, and city. For example, approximately 50% of adults aged 18 to 34 years underwent a medical imaging procedure requiring radiation, whereas 86% of adults 60 to 64 years of age were sent for similar testing. Women also underwent imaging procedures significantly more often than men.

In terms of rates of exposure to moderate and high doses of radiation, 193.8 per 1000 enrollees were exposed to moderate levels of radiation and 18.6 per 1000 enrollees were exposed to high levels. The researchers point out that although most subjects received less than 3 mSv per year, “effective doses of moderate, high, and very high intensity were observed in a sizable minority.”

The Element of Risk

In an editorial accompanying the published study [3], Dr Michael Lauer (National Heart, Lung, and Blood Institute, Bethesda, MD) writes that the number of CT scans obtained has quadrupled since 1992 and that between 1993 and 2001 the number of myocardial perfusion scans increased more than 6% each year, “with no justification for their use based on disease rates, healthcare disparities, or newly published, definitive randomized trials.” Moreover, despite abnormalities on myocardial perfusion scans being powerful predictors of future events, no study has shown that aggressive therapy in these high-risk clients can improve future outcomes, notes Lauer.

Because the use of radiation carries an element of risk, “we need to adopt a new paradigm for our approach to imaging,” writes Lauer. “Instead of investing so many resources in performing so many procedures, we should step back and design and execute desperately needed large-scale, randomized trials to figure out which procedures yield net benefits.”

Lauer argues that with few exceptions, such as mammography, most radiologic testing offers net negative results, because there is little high-level evidence and cumulative exposure can produce real harm, namely radiation-induced cancer.

He contends that physicians should approach imaging with the same “humility” others approached experimental treatments for acute coronary syndromes and that these tests should be subjected to rigorous randomized, controlled, clinical trials. Second, physicians should take a careful history of the client to determine the cumulative dose of radiation a client has already received and provide clear, personalized information about the risks of iatrogenic cancer.

“If we began a national conversation about the dangers of ionizing radiation, it might cause enough discomfort to stimulate demand for high-quality evidence our clients deserve,” writes Lauer.

References

1.Fazel R, Krumholz HM, Wang Y, et al. Exposure to low-dose ionizing radiation from medical imaging procedures. N Engl J Med 2009; 361:849-857.

2.Lauer MS. Elements of danger–the case of medical imaging. N Engl J Med 2009; 361:841-843.