Diagnostic Imaging on the Rise Even in 'Accountable' HMOs

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Radiation Exposure Comes at a Risk

The findings of Dr. Smith-Bindman and his colleagues suggest that when ordering diagnostic tests, physicians must consider, and discuss with patients, the risks of radiation, said Dr. George T. O’Connor and Dr. Hiroto Hatabu.

The number of people who receive high or very high annual exposure to ionizing radiation from imaging studies is not trivial. It may even be appropriate for clinicians to consider the cumulative radiation exposure a given patient has received in recent months or years, they added.

Dr. O’Connor is with the pulmonary center at Boston University and is a contributing editor at JAMA. Dr. Hatabu is in the department of radiology and the center for pulmonary functional imaging at Brigham and Women’s Hospital and Harvard Medical School, Boston. Dr. O’Connor reported no relevant financial disclosures, and Dr. Hatabu reported receiving grant support from Toshiba Medical, Canon, and AZE. These remarks were taken from their editorial comments accompanying Dr. Smith-Bindman’s report (JAMA 2012;307:2434-5).



Advanced diagnostic imaging, with its much higher radiation doses than conventional radiography, is being used with increased frequency even within integrated health care delivery systems that are "clinically and fiscally accountable for their members’ outcomes" – in other words, even in the absence of financial incentives to overuse technologies, according to a report in the June 13 issue of JAMA.

The burgeoning use of diagnostic imaging has been well documented in Medicare and in fee-for-service insured populations, but until now no large, multicenter study has assessed time trends in imaging procedures within HMOs, which supposedly put greater limitations on questionable procedures, said Dr. Rebecca Smith-Bindman of the departments of radiology and biomedical imaging, epidemiology and biostatistics, and ob.gyn. and reproductive sciences, University of California, San Francisco, and her coinvestigators.

"Understanding imaging utilization and associated radiation exposure in these settings could help us determine how much of the increase in imaging may be independent of direct financial incentives," they noted (JAMA 307:2400-9).

The marked increase in advanced imaging is a concern because the higher radiation exposures have been linked with the development of radiation-induced cancers.

Dr. Smith-Bindman and her colleagues performed a retrospective population-based study of imaging trends between 1996 and 2010 among members of six geographically diverse U.S. health care delivery systems: Group Health Cooperative in Washington state; Kaiser Permanente in Colorado, Georgia, Hawaii, and Oregon; and Marshfield Clinic and Security Health Plan in Wisconsin.

Between 933,897 and 1,998,650 patients were included during each year of the study, and they underwent a total of 30.9 million imaging examinations. This averages out to 1.18 imaging studies per patient per year.

The investigators estimated the effective dose of ionizing radiation for each procedure, a measure that includes both the amount of radiation to which the patient is exposed and the biologic effect of that radiation on the exposed organs. They then used that data to calculate the total radiation dose each HMO member received each year, as well as the collective effective dose to the entire population.

The rates of conventional radiography and angiography/fluoroscopy remained relatively stable over the 15-year study period, rising just over 1% each year.

In marked contrast, the number of CT studies tripled, from 52 per 1,000 patients in 1996 to 149 per 1,000 in 2010. This represents an annual growth of nearly 8%.

The number of MRIs quadrupled, from 17 to 65 per 1,000 patients, an annual growth of 10%.

The number of ultrasound exams approximately doubled, from 134 to 230 per 1,000 patients, for an annual growth of 4%.

The rates of nuclear medicine exams decreased slightly, with one notable exception: During the last half of the study period, the number of PET scans skyrocketed from 0.24 per 1,000 patients in 2004 to 3.6 per 1,000 in 2010. This represents an annual growth of 57%.

Not surprisingly, the mean per capita effective radiation dose also rose significantly during the study period, effectively doubling from 1.2 mSv to 2.3 mSv. Among patients exposed to any radiation from medical imaging, the average effective dose climbed from 4.8 mSv in 1996 to 7.8 in 2010.

Of particular concern was the finding that the percentage of patients who received high (over 20-50 mSv) or very high (over 50 mSv) radiation exposure during a given year also approximately doubled. "By 2010, 2.5% of enrollees received a high annual dose of greater than 20-50 mSv, and 1.4% received a very high annual dose of greater than 50 mSv," the investigators wrote (JAMA 2012;307:2400-9).

Putting this exposure level in context, "the National Academy of Sciences’ National Research Council concluded, after a comprehensive review of the published literature, that patients who receive radiation exposures in the same range as a single CT – 10mSv – may be at increased risk for developing cancer," they said.

"The number of patients exposed to such levels highlights the need to consider this potential harm when ordering imaging tests and to track radiation exposures for individual patients so that this information is available to physicians who are ordering tests," Dr. Smith-Bindman and her associates said.

Older patients are at particular risk. The use of imaging, particularly of CT and nuclear medicine exams, increased steeply with patient age. "Among enrollees 45 years and older who underwent imaging, nearly 20% received high or very high radiation exposure annually," the researchers said.

Since the potential harm from such exposure may also increase with patient age, "it is particularly important to quantify the benefits of imaging in these patients," they noted.


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