Aug. 26, 2009
Medical Imaging Can Result in Cumulative Radiation Exposure
Several types of medical imaging procedures- such as x-rays, fluoroscopy, computed tomography (CT) scans, and nuclear medicine scans- expose patients to ionizing radiation, which over time can accumulate to substantial doses, according to a study published this week in the New England Journal of Medicine.
"We know that the use of medical imaging procedures in the US has increased rapidly over the past three decades, resulting in higher average radiation doses for individuals living in the US," summarized Reza Fazel, MD, the lead author of the study and an Emory cardiologist.
This study utilized claims data from UnitedHealthcare on nearly one million adults aged 18 to 65 years old in five regions across the United States to estimate the overall rates of exposure to radiation from medical imaging procedures over a three-year period (2005 through 2007).
Exposure to radiation was estimated for these individuals based on the effective dose (in millisieverts) associated with procedures, a measure that is meant to reflect how harmful a given exposure is to the body on average. Exposure to radiation, especially to doses exceeding 50 to100 mSv, has been associated with a higher risk of developing solid cancers and leukemias years later.
Levels of radiation exposure were categorized by the authors as:
- 'low', less than 3 millisieverts per year, roughly the annual background level from natural sources in the US
- 'moderate', up to 20 millisieverts per year, the 5-year-annual average limit for occupational exposure
- 'high', up to 50 millisieverts per year, the annual limit for occupational exposure
- 'very high' more than 50 millisieverts per year
Nearly 7 out of every 10 adults in the study population underwent at least one imaging procedure associated with radiation exposure during the three-year study period, although the majority of these were low-dose x-rays, such as a chest radiograph. The procedure that contributed most to overall radiation exposure in the population was myocardial perfusion imaging, followed by abdominal, pelvic, and chest CT scans. On average, the effective dose of radiation from all procedures was 2.4 mSv, which is equivalent to approximately 80 percent of the background exposure that the average adult receives in the US from natural sources.
More concerning doses that accumulated over time were uncommon, with doses >20 mSv per year occurring in approximately 2 percent of enrollees and doses >50 mSv per year occurring in 0.2 percent of enrollees. However, Brahmajee Nallamothu, MD, a study author and cardiologist from the University of Michigan cautions that, "Generalizing our results to the total adult population in the US suggests that over 4 million adults are being exposed to >20 mSv per year from these procedures. While the risk to any individual for a single test may be small, the overall risk to the population becomes a concern if one considers the large number of these procedures being performed each year."
One of the key findings of the study was that it confirmed the study released in March of this year by the National Council for Radiation Protection. In addition, the study found that radiation exposure from medical imaging procedures increased with advancing age and was higher in women. CT and nuclear imaging scans accounted for nearly three quarters of the total radiation exposure and over 80 percent of it occurred in the outpatient setting.
Harlan Krumholz, MD, a study author and cardiologist from Yale University, notes that, "People need to be sure that there is value in the testing because it costs both in terms of dollars and radiation exposure."
Kimberly Applegate, MD, an Emory radiologist and radiation safety expert, also adds, "Patients need to ask if the imaging center is accredited, the imaging personnel are credentialed, and the protocols used are weight-based and indication-based to ensure that they receive high-quality imaging. "
The authors caution that they could not comment on clinical indications for the imaging procedures, their appropriateness, or whether other alternative studies were available. Furthermore, effective doses used in the study are averages derived from the literature that are not specific to an individual. Thus, the actual absorbed dose may vary by sex, body mass and body composition, they note. Also, radiation doses may vary by institution and the protocols in current use.
According to the authors, strategies to lower medical radiation exposure to the public are being addressed by national medical physics and radiology organizations, including the American Association of Physicists in Medicine and the American College of Radiology. These strategies include using guidelines to direct more appropriate use of these procedures, using less radiation dose per procedure, and when possible, replacing procedures associated with radiation with other types of imaging, such as sonography or magnetic resonance imaging.
Fazel notes, "Raising both physician and patient awareness on these issues as well as encouraging continued technological advances to lower radiation doses of procedures are the key approaches to lowering long-term risks in patients and for the population. But in the end, these risks need to be balanced against the immediate clinical need for these procedures, which are substantial in many cases."
The Robert W. Woodruff Health Sciences Center of Emory University is an academic health science and service center focused on missions of teaching, research, health care and public service. Its components include the Emory University School of Medicine, Nell Hodgson Woodruff School of Nursing, and Rollins School of Public Health; Yerkes National Primate Research Center; Emory Winship Cancer Institute; and Emory Healthcare, the largest, most comprehensive health system in Georgia. Emory Healthcare includes: The Emory Clinic, Emory-Children's Center, Emory University Hospital, Emory University Hospital Midtown, Wesley Woods Center, Emory University Orthopaedics & Spine Hospital, the jointly owned Emory-Adventist Hospital, and EHCA, a limited liability company created with Hospital Corporation of America. EHCA includes two joint venture hospitals, Emory Eastside Medical Center and Emory Johns Creek Hospital. The Woodruff Health Sciences Center has a $2.3 billion budget, 18,000 employees, 2,500 full-time and 1,500 affiliated faculty, 4,300 students and trainees, and a $5.5 billion economic impact on metro Atlanta.