Abdominal CT Radiation Risk

Patients with inflammatory bowel disease (IBD) and other gastrointestinal disorders can be exposed to high levels of radiation—mostly from abdominal computed tomography (CT) scans—reports the March issue of Clinical Gastroenterology and Hepatology.

Access to high-quality facilities and technologic advances have increased the use of CT imaging of the GI tract. However, CT uses higher levels of ionizing radiation than other imaging approaches. This is a cause for concern, because protracted exposure to low levels of ionizing radiation could increase lifetime risk of malignancy. The use of diagnostic radiation across a broad range of GI disorders has not been analyzed.

Alan Desmond et al. examined the use of diagnostic imaging in 2590 patients with GI disorders over a 10-year period, estimating the cumulative effective dose (CED) of diagnostic radiation received by patients with IBD, other organic GI disorders and functional GI disorders.

They found that 57% of the patients with these disorders underwent diagnostic imaging. Over the past decade, patients’ mean annual radiation exposure increased, from 2.2 mSv/annum in 1999–2000, to 3.1 mSv/annum in 2008–2009 (see figure).

Annual number of imaging studies performed per 100 patients; (B) annual diagnostic radiation exposure per patient, 1999–2009 (2509 patients)

The greatest increase in exposure came from CT imaging, from 0.9 mSv/annum to 1.8 mSv/annum.

Annual diagnostic radiation exposure exceeded that of background radiation from natural sources for 54.5% of the subjects (background radiation exposure is approximately 2.9 mSv/annum in the US and Europe).

Patients with Crohn’s disease had the highest total CEDs (>30.8 millisieverts), followed by those with ulcerative or indeterminate colitis, organic small bowel disorders, organic hepatic disorders or patients that had developed functional disorders as children.

Desmond et al. concluded that individuals with IBD and other functional GI disorders are exposed to higher-than-normal annual and overall levels of diagnostic radiation, and that evidence-based guidelines to reduce radiation exposure are needed.

Large epidemiologic studies of populations of atomic bomb survivors and workers in the nuclear industry have associated radiation exposure with increased cancer risk; risk increases with cumulative exposure in a linear fashion.

Most subjects in the study population received cumulative exposures of less than 30 mSv—it is not clear if this level of exposure poses a health risk. However, experts agree that cumulative radiation exposures exceeding 50–100 mSv are not safe. Cumulative exposures of this magnitude were observed in almost 10% of subjects in the study.

The most concerning finding might be that more than half of patients with cumulative exposure that exceeded the 90th percentile were younger than 35 years old. Based on US National Academy of Science estimates and individual patient cumulative exposures, the lifetime excess relative risk of developing malignancy in these individuals would be about 1%–15%. Furthermore, most of the patients in the high cumulative exposure group had IBD, which also increases lifetime risk of GI malignancy.

Desmond et al. state that the clinical benefits of diagnostic imaging of the GI tract are not in doubt—particularly for patients with Crohn’s disease, who often undergo abdominal imaging to determine the extent of their disease and detect extramural complications. However, the use of diagnostic imaging in patients with functional GI disorders has not been carefully studied, so its benefits to this population are not clear.

Alternative, radiation-free imaging modalities include ultrasound, capsule endoscopy, and magnetic resonance imaging (MRI). Strategies are also being developed to reduce the radiation dose associated with CT imaging—some by as much as 60%. These are being examined in clinical trials.

Limitations of the study include that the data was collected from patients analyzed at a tertiary gastroenterology center that specializes in IBD and functional GI disorders, so patients were likely to have severe or complicated diseases. Furthermore, the actual dose of radiation received by a patient during imaging can vary, based on the equipment, imaging technique, patient’s body and other technical factors.

In an editorial that accompanies the article, Lincoln Berland reminds gastroenterologists to be aware of the patient’s history of exposure when requesting new examinations. He says that the effort conducted by Desmond et al. to increase awareness of cumulative radiation exposure for patients with GI disorders is extremely useful, and that decisions about individual examinations or alternative strategies should be based on careful analysis of benefit vs. risk.

Desmond et al. say that due to the likely deleterious effects of exposure to ionizing radiation and the age and sex of many patients with these diseases, there is a clear need for evidence-based guidelines on the use of diagnostic imaging in patients with organic and functional GI disorders.

Read the article online. This article has accompanying CME activities.
Desmond AN, McWilliams S, Maher MM, et al. Radiation exposure from diagnostic imaging among patients with gastrointestinal disorders.  Clin Gastroenterol and Hepatol 2012;10:259–265.

Read the accompanying editorial.
Berland LL. Benefits of computed tomography versus risks of radiation for organic gastrointestinal conditions.  Clin Gastroenterol and Hepatol 2012;10:216–217.

About Kristine Novak, PhD, Science Editor

Dr. Kristine Novak is the science editor for Gastroenterology and Clinical Gastroenterology and Hepatology, both published by the American Gastroenterological Association. She has worked as an editor at biomedical research journals and as a science writer for more than 12 years, covering advances in gastroenterology, hepatology, cancer, immunology, biotechnology, molecular genetics, and clinical trials. She has a PhD in cell biology and an interest in all areas of medical research.
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1 Response to Abdominal CT Radiation Risk

  1. Pingback: Clinical Updates Week of March 17, 2012 « Clinical Advances

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