Study:
Diagnostic X-ray Exposure Risk Low
Findings Link Diagnostic Imaging to 1% of Cancers in U.S.
and 3% in Japan
Jan. 29, 2004 -- Roughly one in 100 cancers in the U.S. are
caused by exposure to medical X-rays, according to the most
detailed study of radiation risk associated with diagnostic
imaging ever conducted.
Conventional X-rays and imaging techniques such as computed
tomography (CT) are the largest man-made source of radiation
exposure. While the benefits of these diagnostic tools are well
established, the risks have been harder to quantify.
"There have been relatively few studies looking at this
issue," University of Oxford research fellow Amy Berrington
de Gonzalez, PhD, tells WebMD. "It is generally accepted
that their use is associated with a small increase in cancer
risk, but the extent of that risk has not been clear."
Estimates of Cancer Risks
Berrington de Gonzalez and colleague Sarah Darby, estimated
the likely extent of cancer risk for 15 industrialized countries,
based on the annual number of diagnostic X-rays given each year.
People in Japan had the highest risk, because they underwent
more diagnostic imaging procedures than people in any of the
other studied countries -- 1,477 for every 1,000 people. That
compares with:
* 1,254 X-rays annually per 1,000 people in Germany
* 962 X-rays annually per 1,000 people in the U.S.
* 565 X-rays annually per 1,000 in people Australia
The researchers concluded that almost 7,600 cancers diagnosed
each year in Japan, or 3.2% of the total cancer cases, are linked
to diagnostic imaging procedures.
The people in the U.K. had the lowest risk, with just 489 X-rays
conducted each year for every 1,000 people. The researchers
estimate that the lifetime risks attributed to radiation exposure
from diagnostic X-rays is roughly 0.6% in the U.K. That translates
to roughly 700 of the 124,000 cancer cases identified in the
country each year. The findings are published in the Jan. 31
issue of the journal The Lancet.
They also estimate that in the U.S. the lifetime risk of cancer
caused by radiation exposure from X-rays is approximately 0.9%.
That is almost double the risk suggested in one of the only
other studies ever to examine the issue, published in 1981.
This lifetime risk accounts for about 5,700 cancers per year.
Risk Estimate Challenged
In an accompanying editorial, University of Munich radiologist
Peter Herzog and oncologist Christina T. Rieger write that the
researchers did not assess the indications or benefits achieved
for patients in X-ray examinations. Benefits include the earlier
detection of cancers by radiological examinations and the possibility
of early treatment, which probably allows more cure of cancers
than radiological exposure is able to cause.
Herzog tells WebMD the study used cancer rate information from
Japanese bomb survivors as a model to study the risks of cancer
from diagnostic X-ray exposure. They had very different exposures,
most notably those associated with ingesting contaminated food,
water, and dust.
"The problem is that these bomb survivor data are really
the only studies examining radiation exposures in a large population,"
he says. "But we believe that relying on them leads to
a very great overestimation of the real risk."
Even though he believes the risk is probably minimal, Herzog
says clinicians should take steps to limit their patients' radiation
exposure by reducing unnecessary X-rays and CTs.
"Up to 30% of chest X-rays may not
be indicated; unnecessary CT examinations can lengthen
hospital stays as well as causing radiation exposure,"
Herzog and Rieger wrote in their editorial. "In everyday
practice, those ordering radiological procedures should think
carefully about the benefit for and the risk to their patients
for each examination."
SOURCES: Berrington de Gonzalez et al., The Lancet, Jan 31,
2004; vol. 263: pp - 345-351. Amy Berrington de Gonzalez, PhD,
research fellow, University of Oxford, Oxford, U.K. Peter Herzog,
MD, radiologist, University of Munich. Christina Rieger, MD,
oncologist, University of Munich.
