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Do computed tomography scans cause cancer?

The risk of developing cancer from radiology procedures such as x-rays, computed tomography (CT) scans, or nuclear medicine scans is a current hot topic in medicine. Although the relationship of exposure to ionizing radiation and cancer has been studied extensively, the current concern is fueled by a rapid rise in the number of CT scans being performed. CT scans expose a person to more radiation than a diagnostic x-ray.

Radiation dose is expressed as the absorbed dose in gray (Gy). However, the effective dose, measured in miliSieverts (mSv), takes into account the radiosensitivity of each organ. For example, a pediatric chest x-ray may have an effective dose from 0.01-0.02 mSv, compared to a chest CT dose of 2-4 mSv (Chong et al., 2010). Comparison of the effective doses of different radiographic procedures to levels of background radiation (natural occurring radiation that is constantly present in the environment) provides context to understand the significance of exposure. The average person is exposed to 2.4-3 mSv of background radiation each year, and a seven-hour plane ride exposes a person to 0.02 mSv.

Berrington de Gonzalez and Darby (2004) published one of the first studies estimating the risk of cancer from diagnostic x-rays. They developed a risk model based on data from Japanese survivors of the atomic bomb. The model was used on current x-ray data from 15 developed countries. In 14 of the countries, the cumulative risk of cancer from diagnostic x-rays was estimated to be 0.6%-1.8%, equivalent to 700-2,100 cases of cancer per year, but in the 15th country, Japan, the risk was more than 3%. In a separate study, Berrington de Gonzalez et al. (2009) looked at data for the approximately 72 million CT scans that were performed in the United States in 2007. From this, they estimated that 29,000 future cancers could be related just to those scans.

Another point of concern is the wide range of radiation doses. Smith-Bindman et al. (2009) retrospectively looked at radiation doses for the 11 most common CT scans at four institutions in the San Francisco Bay area. They found a 13-fold variation between the highest and lowest doses for each scan. The researchers recommended standardizing radiation doses for the different scans. Mammography radiation doses are already regulated by the U.S. Food and Drug Administration, but at this time, it does not regulate CT radiation doses.

The American College of Radiology has started an awareness program called Image Wisely (www.imagewisely.org) to encourage practitioners to avoid unnecessary scans or to use the lowest radiation doses possible when scans are needed. The pediatric campaign is called Image Gently (www.pedrad.org/associations/5364/ig). Children are at particular risk because of their longer life expectancy, more active cell division, and higher organ doses at a lower body mass (Chong et al., 2010). Concerned patients can keep track of radiology tests using sites such as http://xrayrisk.com or by downloading record forms at www.imagewisely.org.

CT scans have improved medical care and have lessened more invasive procedures. For patients, the benefits usually outweigh the risks. Giving thoughtful consideration of the need for CT scan is suspected, although not proven, to reduce radiation exposure for patients. Partnering with a radiologist can help to decide the most appropriate radiology test to obtain the necessary information.

Berrington de Gonzalez, A., & Darby, S. (2004). Risk of cancer from diagnostic x-rays: Estimates for the UK and 14 other countries. Lancet, 363, 345-351.

Berrington de Gonzalez, A., Mahadevappa, M., Kim, K., Bhargavan, M., Lewis, R., Mettler, F., & Land, C. (2009). Projected cancer risks from computed tomographic scans performed in the United States in 2007. Archives of Internal Medicine, 169, 2071-2077.

Chong, A.L., Grant, R., Ahmed, B., Thomas, K., Connolly, B., & Greenberg, M. (2010). Imaging in pediatric patients: time to think again about surveillance. Pediatric Blood and Cancer, 55, 407-413.

Smith-Bindman, R., Lipson, J., Marcus, R., Kim, K., Mahesh, M., Gould, R., ... Miglioretti, D.L. (2009). Radiation dose associated with common computed tomography examinations and the associated lifetime attributable risk of cancer. Archives of Internal Medicine, 169, 2078-2086.

[By Susan Pillet, RN, CPNP, CPON[R], Contributing Editor]
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Title Annotation:straight talk
Author:Pillet, Susan
Publication:ONS Connect
Geographic Code:1USA
Date:Mar 1, 2011
Words:698
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