April 2009

Cardiac CTs expose patients to high radiation dose

Use of the imaging technique known as cardiac computed tomography (CT) angiography (CCTA) has the potential to expose patients to high doses of radiation -- equivalent to as many as 600 chest x-rays -- according to a study in the February 4, 2009 issue of JAMA.

The 64-slice (able to scan 64 images per rotation) CCTA has emerged as a popular diagnostic imaging method for the assessment of coronary artery disease and has been proposed for evaluating patients in emergency departments with chest pain.

Many clinicians, however, may still be unfamiliar with the magnitude of radiation exposure that is received during CCTA in daily practice and with the factors that contribute to radiation dose, according to background information in the article.

Researchers investigated the magnitude of radiation dose of CCTA in daily practice, factors contributing to radiation dose and the use of currently available strategies to reduce radiation dose. The trial involved 1,965 patients undergoing CCTA between February and December 2007.

Analysis was used to identify independent predictors associated with radiation dose, which was measured as dose-length product (DLP; equals the average radiation dose over a specific investigated volume multiplied by the scan length), which best mirrors the radiation a patient is exposed to by the entire CT scan, according to the authors.

The researchers found that the median DLP of the patients in the study was 885 mGy x cm (a measurement of absorbed radiation), which corresponds to an estimated radiation dose of 600 chest x-rays.

"The study results reinforce the observation that cardiac CT angiography (CTA) is still a potentially high-dose procedure, and like all procedures involving the use of ionizing radiation, a patient-specific benefit-risk analysis should always be performed to justify the imaging study," commented Andrew J. Einstein, MD, Ph., of the Columbia University College of Physicians and Surgeons, New York, in an accompanying editorial.