Less Is More
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH , Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips is a retained consultant for Cephalon and Ventus, and serves on the speakers bureaus for Cephalon and Boehringer Ingelheim.
Synopsis: Imaging procedures are an important source of exposure to ionizing radiation in the United States and can result in high cumulative effective doses of radiation.
Source: Fazel R, et al. Exposure to low-dose ionizing radiation from medical imaging procedures. N Engl J Med 2009;361:849-857.
This study is the result of a retrospective look at claims data from the UnitedHealthcare systems in Arizona, Dallas, Orlando, Florida, and Wisconsin. The investigators included all enrollees between 18 and 64 years of age who were alive and continuously enrolled in a plan administered by UnitedHealthcare over a 3-year period ending in 2007. All claims were examined for Current Procedural Terminology (CPT) codes that identified imaging procedures involving radiation exposure, regardless of indication. Radiation that was specifically delivered for a therapeutic purpose (e.g., high-dose radiation therapy for breast cancer) was excluded. The authors corrected for the potential of overestimating the radiation dose from procedures that were performed on the same day, and excluded the nonspecific CPT code 76499, for "unlisted radiographic procedure." Estimates of typical effective doses (assessed in milliSieverts [mSv]) for each imaging procedure were obtained from published literature. For most common procedures, data were summarized in a recent review.1 Cumulative effective doses of radiation were calculated for the entire study population over the 3-year study period. The authors calculated population-based rates of effective doses for the study population overall and for each age-based and sex-based group.
There were nearly a million (952,420) subjects in the study population. Their mean age was 35.6 years, and 52.4% were women. Sixty-eight percent of the patients underwent at least one imaging during the 3-year study period, with a mean of 1.2 ± 1.8 procedures per person per year. The proportion of subjects undergoing at least one procedure during the study period was higher in older people, rising from 49.5% of those who were ages 18-34 years to 85.9% of those who were ages 60-64 years. Women underwent procedures significantly more often than men, with a total of 78.7% of women undergoing at least one procedure during the study period, as compared with 57.9% of men. The mean effective dose was 2.4 ± 6.0 mSv per person per year, and the median effective dose was 0.1 mSv per person per year.
Moderate doses of radiation were seen at an annual rate of 193.8 per 1000 enrollees, whereas high and very high doses were incurred at an annual rate of 18.6 and 1.9 per 1000 enrollees, respectively. These rates rose with advancing age. In addition, women were more likely than men to have higher rates of high and very high doses up to the age of 50 years.
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The top 5 procedures in terms of the cumulative effective radiation dose are listed in the Table (above).
Myocardial perfusion studies alone accounted for more than 22% of the total effective dose, and CT of the abdomen, pelvis, and chest accounted for nearly 38%. On the other hand, plain radiography procedures made up 71.4% of the total number of procedures performed but only 10.6% of the total effective dose. Overall, 81.8% of the total effective dose was delivered in outpatient settings, most often in physicians' offices.
Commentary
This study, albeit conducted by an entity with a vested interest in reducing health care procedures and costs, ought to make us stop and think about the necessity and utility of radiographic procedures. This is especially true in the face of proliferating, free-standing "imaging-on-demand" facilities, such as those who screen worried smokers for abnormal chest CT findings. It behooves us to remember (and to remind our patients) that evidence links exposure to low-dose, ionizing radiation with the development of solid cancers and leukemia.2 Whereas health care professionals are carefully monitored and restricted to effective doses of 100 mSv every 5 years (i.e., 20 mSv per year), patients are not. Indeed, studies of patient data on longitudinal radiation exposure from diagnostic radiographic procedures are few and far between, even though these types of procedures may be performed multiple times in the same patient. In this study, the authors conclude, "Generalization of our findings to the nonelderly adult population of the United States suggests that these procedures lead to cumulative effective doses that exceed 20 mSv per year in approximately 4 million Americans. "
In the United States, the per capita dose of radiation from medical imaging has increased steadily in the past 3 decades.3,4 The current study focused on non-elderly adults, for whom the long-term risks of radiation are most relevant, since the related risks accrue over a lifetime.5 The investigators found that excess radiation exposure is more likely to occur in women than in men, which is of particular concern, since cancer may be more likely to develop in women than in men after similar levels of exposure.6
Recommendations related to medical exposures to radiation have focused on justifying each procedure and optimizing its use to ensure that exposure is "as low as reasonably achievable."7,8 Ultimately, it is up to the ordering physician to recognize the risk and discuss it with the patient when radiographic procedures are being considered. In a study of health care providers using CT in patients with abdominal and flank pain, fewer than half of radiologists and only 9% of emergency department physicians reported even being aware that CT was associated with an increased risk of cancer.9
We need to do better than this!
References
1. Mettler FA Jr, et al. Effective doses in radiology and diagnostic nuclear medicine: A catalog. Radiology 2008;248:254-263.
2. National Research Council. Health risks from exposure to low levels of ionizing radiation: BEIR VII phase 2. Washington, DC: National Academies Press; 2006.
3. National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States: Recommendations of the National Council on Radiation Protection and Measurements. Report No. 160. Bethesda, MD: NCRP; March 2009.
4. Mettler FA Jr, et al. Medical radiation exposure in the U.S. in 2006: Preliminary results. Health Phys 2008;95:502-507.
5. Wennberg JE, et al. Use of hospitals, physician visits, and hospice care during last six months of life among cohorts loyal to highly respected hospitals in the United States. BMJ 2004;328:607.
6. Einstein AJ, et al. Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography. JAMA 2007;298:317-323.
7. United States Nuclear Regulatory Commission. Regulation (10 CFR), subpart B 20.1101: Radiation protection programs. Washington, DC: Nuclear Regulatory Commission; 1998.
8. Prasad KN, et al. Radiation protection in humans: Extending the concept of as low as reasonably achievable (ALARA) from dose to biological damage. Br J Radiol 2004;77:97-99.
9. Lee CI, et al. Diagnostic CT scans: Assessment of patient, physician, and radiologist awareness of radiation dose and possible risks. Radiology 2004; 231:393-398.