Medical Imaging Radiation Can Accumulate Overtime
Many types of medical imaging procedures, such as x-rays, computed tomography 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 radiation is not benign and some people are getting high exposures,” says Reza Fazel, M.D., the lead author of the study and a cardiologist at Emory University.
Researchers used claims data from UnitedHealthcare on nearly 1 million individuals 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.
The study was led by a team of doctors from several academic medical centers, including Emory University, the University of Michigan Health System, and Yale University.
Exposure was estimated for these individuals based on the effective dose (in millisieverts) of radiation associated with the procedure, a measure that is meant to reflect how harmful a given exposure is to the body on average. Exposure to radiation has been linked to higher rates of solid cancers and leukemias.
Levels of radiation exposure were categorized as:
* low, less than 3 millisieverts per year, roughly the background level from natural sources in the US
* moderate, up to 20 millisieverts per year, the annual limit for average occupational exposure over five years
* high, up to 50 millisieverts per year, the annual limit for occupational exposure
* very high, more than 50 millisieverts per year.
Nearly eight 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.
On average, the effective dose of radiation from these procedures was 2.4 mSv per year, resulting in overall radiation exposures in the average adult in the United States that almost doubled what would be expected from natural sources alone, the authors wrote.
More concerning doses (>20 mSv per year) that accumulated over time were not uncommon. For instance, the authors stated that, if their findings are generalized to the total adult population of the United States, this level of exposure may occur in over 4 million adults.
“It is important to note that we are talking about radiation doses that are incurred in one year,” says study author Brahmajee K. Nallamothu, M.D., cardiologist at the U-M Cardiovascular Center and researcher at the UM/VA Patient Safety Enhancement Program. “Cumulative doses over a lifetime may be much higher.
“This becomes particularly concerning when you consider that over a third of individuals who received moderate and high effective doses were under the age of 50- because the long-term risks of developing cancer from radiation will be higher in younger individuals,” Nallamothu says.
“We do not want to scare people or have them refuse needed imaging procedures because of this work,” added Harlan Krumholz, M.D., a study author and cardiologist at Yale. “However, people need to be sure that there is value in the testing because it costs both in terms of dollars and radiation exposure.”
One of the key findings of the study was that radiation exposure from medical imaging increased with advancing age and was higher in women.
CT and nuclear imaging scans accounted for nearly three quarters of the overall radiation exposure in the study and over 80 percent of the radiation exposure occurred in the outpatient setting.
The authors caution that they could not comment on indications for the imaging procedures, their appropriateness, or whether other alternative studies were available. Furthermore, effective doses used in the study are calculated doses that are not specific to an individual, but are estimated based on an ”average” 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.
The authors conclude by calling for better strategies to optimize and ensure the appropriate use of these procedures in the general population.
“Raising both physician and patient awareness regarding these issues as well as encouraging continued technological advances to lower radiation doses of procedures are the key approaches to lowering risks in patients,” Fazel says.