SNM, medical physicists react to imaging radiation report

The American Association of Physicists in Medicine (AAPM) has offered to provide the public with additional background information to help avoid a misinterpretation of the findings contained in a report issued March 3 by the National Council on Radiation Protection and Measurements (NCRP). Additionally, the Society of Nuclear Medicine (SNM) has urged Americans to consider the benefits of medical imaging.

"The report is not without scientific controversy and requires careful interpretation," the AAPM said.

The NCRP examines the various sources of ionizing radiation in the United States, estimates the total amount of radiation delivered in 2006, and compares those amounts to the estimates published in 1987. While the naturally-occurring amounts of radiation have changed little in the last two decades, there has been a dramatic increase in the amount of radiation from medical imaging procedures, including CT and cardiac nuclear medicine exams.

However, AAPM said the report does not "attempt to quantify the associated health risks nor specify the actions that should be taken in light of these latest data." AAPM experts have cautioned that these data do not necessarily indicate that the U.S. population is at any higher risk due to an increased use of medical imaging.

They caution that the new report should not deter patients from getting medically-appropriate imaging exams. "The NCRP findings on average population dose could be easily misinterpreted if applied to an individual patient's medical situation," they wrote.

In the last few years, reports in the medical literature and in the press have affected public perceptions of CT scans by raising questions of risk related to the use of x-rays, which in high doses have the potential to damage cells and cause cancer.

The NCRP report falls squarely into this controversy because it estimates the total U.S. exposure to all sources of ionizing radiation has increased six-fold since 1980 -- with about half of this increase due to CT scans.

"This increase is easily misinterpreted, however, because the report calculates the total radiation dose for all CT scans performed in 2006 and divides that by the U.S. population for that year," the AAPM stated. "What is not considered in this global averaging approach is that CT scans are given disproportionally to certain people and groups -- for example, the elderly, people admitted to hospitals for serious trauma, and cancer patients having scans to evaluate their response to treatment."

"Adding up all the doses and then spreading out the total over the entire population, no matter a person's age, occupation, location, or health status is not appropriate for assessing risk to the general population," said Cynthia McCollough, PhD, FAAPM, FACR, professor of radiological physics at the Mayo Clinic and chair of an AAPM Task Group that issued a CT radiation dose-management report last year. "The NCRP report is very clear in this regard. The data summarize the sources and amounts of radiation exposure in the U.S. and the total values are normalized to the total U.S. population. The values reported are not appropriate for estimating potential health effects."

"Nuclear medicine and molecular imaging hold great promise for diagnosis and tailoring treatments for patients with cancer, neurological or cardiovascular disorders," said Robert W. Atcher, PhD, president of SNM. "We support giving patients the care they need by qualified, accredited nuclear medicine and molecular imaging physicians."

To further protect patients, Atcher said the society is actively collaborating with other organizations representing oncologists, cardiologists, radiologists and other medical professions to ensure that physicians and technologists are adequately trained and credentialed prior to performing a nuclear medicine procedure.