A review article, Computed Tomography -- An Increasing Source of Radiation Exposure, published in the November 29, 2007 issue of The New England Journal of Medicine asserts that the radiation from computed tomography (CT) may cause up to 2% of all cancers in the United States.

Background

A CT scan creates a three-dimensional picture of the inside of the body using a series of x-ray pictures that are taken from many different angles. A computer compiles these images into a detailed, cross-sectional view. Because CT scans have proven so useful and beneficial in the practice of medicine, the use of CT has steadily increased. In the article, the authors cite data estimating that 62 million CT scans a year are done in the United States.

The fact that radiation exposure increases cancer risk has been well-studied, especially in atomic bomb survivors. It is well known that diagnostic x-rays and CT expose people to low levels of radiation. The concern raised in this study is that the amount of radiation delivered through CT is many times higher than any other radiology test.

Using published data, the authors estimated how much radiation is delivered by a CT examination. By applying data from the atomic bomb exposure studies, the authors extrapolated the number of cancer cases that might result from CT exposure. With the increasing use of CT, 1.5% to 2% of all cancers theoretically may be caused by CT, the authors concluded.

Additional perspective

“This is a compelling article that raises interesting and important issues,” said Allen S. Lichter, MD, Executive Vice President and CEO of ASCO. “Although some are questioning the methodology of this article, it is important to reduce cancer risks where possible, and the recommendations in the article are reasonable.”

The recommendations mentioned in the article include lowering the CT-related dose for each patient, replacing CT use, when practical, with other options, such as ultrasonography (ultrasound) and magnetic resonance imaging (MRI, a test that uses electromagnetic waves to create pictures of the inside of the body), and decreasing the number of CT studies that are prescribed.

Bottom line

“This review reminds us that doctors and patients must always consider the possible risks and benefits--both immediate and long term--for any medical intervention. For patients with active cancer, CT scanning is usually beneficial, but we should always consider how it will enhance care and whether other tests that involve less radiation exposure can be substituted,” said Nancy Davidson, MD, ASCO President and Director of the Breast Cancer Program at the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University in Baltimore, Maryland.

“The most important message is that when a CT scan is needed for diagnosis, especially for the management of cancer, the benefits always exceed the risks. But, other imaging methods should be used when they can provide the same benefit with less radiation exposure,” added Gabriel Hortobagyi, MD, FACP, ASCO’s Immediate Past President and Chair of the Department of Breast Medical Oncology at the University of Texas M. D. Anderson Cancer Center in Houston.

Dr. Lichter agreed, “CT can save lives and in the cases where it is important for patients' medical care, the benefit and information gained far outweighs the risk. CT is certainly getting better as technology improves and lower doses are being used. However, CT should only be used when medically necessary.”

What This Means for Patients

The American College of Radiology (ACR) has information for both physicians and their patients at www.radiologyinfo.org and recommends that patients keep a record of their x-ray and CT scan history and talk with their doctor about the rationale for the CT scan if one is recommended. The ACR also provides accreditation of facilities with x-ray technology and defines criteria for providing the most appropriate imaging scan. Additionally, the Radiological Society of North America (RSNA) has relevant information about the use of CT and other imaging tests at www.rsna.org.

Reference

Brenner, DJ; Hall, EJ. Computed tomography—An Increasing Source of Radiation Exposure. The New England Journal of Medicine, 2007; 357:2277-2284

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