Scientists disagree as to whether there is a threshold below which there is no risk. Most experts, including the national academy, accept a "linear no-threshold model" which states that the less the radiation, the less the risk but there is no completely safe threshold.
The problem, said Daniel Low, science council chair of AAPM, is that extrapolation for very low dose assessments of cancers or death, is "inaccurate, unscientific and leads to concern by patients." Such predictions of cancer and deaths from low doses are "speculative," AAPM says in its statement.
People don't understand the uncertainties, Low said.
The situation is made worse by journalists who confuse relative risk with absolute risk in their stories. If the mortality of a disease increases from two persons per 100,000 to four per 100,000, it is true that the relative risk has doubled, but the absolute risk remains very low.
"I wish that all journalists, including science journalists, did a better job of reporting on risk, of making sure that our stories always were set within a realistic perspective," said Deborah Blum, a Pulitzer-Prize winning science writer who now teaches at the University of Wisconsin at Madison. "Far too often we end up scaring people unnecessarily or focusing attention on unlikely risk scenarios and distracting from the major ones ... Journalists as a pack tend to pick up the different, the dramatic, the one in a million chance of mortality."
Other organizations seem to agree with the AAPM statement.
"We believe that risk of radiation exposure from diagnostic imaging is much less than the risk of not having the examination if the examination is diagnostically warranted," said Penny Butler, senior director at the American College of Radiology.
Mary Mahoney, chair of public information at the Radiological Society of North America and a radiologist at the University of Cincinnati Medical Center, said her organization agrees completely with AAPM and is revising its position on its website to link to the AAPM.
"I don't want anyone not to get critically important information because of fear of the radiation," said Mahoney.
Smith-Bindman said part of the problem is that sometimes the devices are used when they are not necessary, a situation peculiar to the American medical system. In the United Kingdom and Europe the devices are not used unless the need is warranted by the patient's medical condition.
On that, everyone seems to agree.
"[AAPM] acknowledges that medical imaging procedures should be appropriate and conducted at the lowest radiation dose consistent with acquisition of the desired information," the organization said in a press release.
Editor's Note: Inside Science is supported by the American Institute of Physics, of which the American Association of Physicists in Medicine is one of ten member societies.
Joel Shurkin is a freelance writer based in Baltimore. He was science editor of the Philadelphia Inquirer and was on a team that won a Pulitzer Prize for coverage of Three Mile Island