Medical imaging exposes a significant portion of patients to various doses of ionizing radiation, and in some cases, to substantial doses, potentially increasing the associated risk of cancer, according to findings of a retrospective cohort study.
The results are based on an analysis of 952,420 nonelderly adults who were enrolled in United Healthcare's database between 2005 and 2007, and living in one of five U.S. markets: Arizona, Dallas, Orlando, South Florida, and Wisconsin.
Roughly 70% of the study population underwent at least one imaging exam during the 3-year study period, “resulting in mean effective doses that almost doubled what would be expected from natural sources alone,” wrote Dr. Reza Fazel of the division of cardiology at Emory University, Atlanta, and her coinvestigators.
Although most patients received less than 3 millisievert (mSv) per year—which was considered low exposure—there was a sizable minority of patients who received moderate, high, or very high radiation doses, they wrote.
CPT codes for imaging procedures involving radiation were used to identify claims from hospitals, outpatient facilities, and physicians' offices. They excluded procedures in which radiation was specifically delivered for therapeutic purposes, such as high-dose radiation for cancer.
Procedures were categorized by technique: plain radiography, CT, fluoroscopy (including angiography), and nuclear imaging. They also categorized the procedures by area of focus: chest (including cardiac imaging), abdomen, pelvis, arm or leg, head and neck (including brain), multiple areas (including whole-body scanning), and unspecified.
In all, 3,442,111 imaging procedures associated with 655,613 patients were identified in the 3-year period. The average number of procedures per person per year was 1.2 and median number was 0.7 per person per year. The mean effective dose was 2.4 mSv/person per year with a median effective dose of 0.1 mSv/year.
The proportion of patients undergoing at least one procedure during the study period increased with age, from 50% in those aged 18-34 years to 86% in those aged 60-64 years. A total of 79% of women underwent at least one procedure during the study period, compared with 60% for men (N. Engl. J. Med. 2009;361:849-57).
Moderate doses (3-20 mSv/year, the upper annual limit for occupational exposure for at-risk workers, averaged over 5 years) occurred at an annual rate of 199 per 1,000 patients. High (20-50 mSv/year, the upper annual limit for occupational exposure for at-risk workers in any given year) and very high (greater than 50 mSv/year) doses occurred at annual rates of 19 and 2 per 1,000 patients, respectively. “Each of these rates rose with advancing age,” noted Dr. Fazel.
“Generalization of our findings to the United States suggests that these procedures lead to cumulative effective doses that exceed 20 mSv per year in approximately 4 million Americans,” the researchers wrote.
By anatomical site, chest procedures accounted for 45% of the total effective dose. Lastly, the bulk of the total effective dose—82%—was delivered in outpatient settings, primarily physicians' offices.
The findings are concerning, particularly for patients who undergo several imaging tests in a short period of time, Dr. Michael S. Lauer wrote in an accompanying editorial (N. Engl. J. Med. 2009;361;841-3).
Despite the cumulative risk associated with radiation exposure, it's generally not something that is discussed with patients undergoing an imaging procedure, noted Dr. Lauer, who is director of the Prevention and Population Sciences Division of the National Heart, Lung, and Blood Institute. “The issue of radiation exposure is unlikely to come up because each procedure is considered in isolation, the risks posed by each procedure are low and seemingly unmeasurable, and any radiation-induced cancer won't appear for years and cannot easily be linked to past imaging procedures.”
“The exposure of patients cannot be restricted, largely because of the inherent difficulty in balancing the immediate clinical need for these procedures, which is frequently substantial, against stochastic risks of cancer that would not be evident for years, if at all.”
Dr. Fazel reported that she has no relevant conflicts of interest, although several of her coauthors reported significant relationships with pharmaceutical and medical imaging companies. Dr. Lauer reported that he has no relevant conflicts of interest.