[ RadSafe ] AAPM Response to NEJM article on CT scans and cancer risk

Sat Dec 1 16:56:51 CST 2007

At http://www.aapm.org/announcements/CTScans.asp

The AAPM Statement on Radiation Dose from Computed
Tomography, in response to the Brenner and Hall NEJM
article published Nov 29, 2007. 

A recent article by Drs. David Brenner and Eric Hall
in the New England Journal of Medicine1 has suggested
that the radiation dose from CT scans is a cause for
concern, and may be responsible for a small percentage
of cancer deaths in the United States. While the
conclusions of the Brenner article have been portrayed
by some as conclusive, in reality the scientific
community remains divided in regards to the radiation
dose effects of CT. The AAPM is an organization of
6700 Medical Physicists, and radiation dosimetry in CT
and other sources of x-ray exposure is the core
expertise of the vast majority of our members. Dr.
Brenner’s article correctly points out that the use of
CT is increasing at an exponential rate, and that CT
should not be used for medical indications that are
not warranted or serious. The AAPM adamantly concurs
with these observations, and has long advocated that
CT should be used judiciously and only when medically
indicated. For example, the AAPM policy paper on CT
screening has recommended against “CT screening” for
many years. 

However, the medical information that is derived from
appropriate diagnostic CT scans literally and
emphatically saves the lives of thousands of Americans
on a daily basis, for patients who have experienced
severe trauma such as in an automobile accident, for
patients who have blood clots in their lungs
(pulmonary embolisms), and for a vast array of other
medical indications. The Brenner article illuminates
many issues of importance in regards to CT, but the CT
experts in the AAPM feel that much of the message of
this article may be misconstrued or misunderstood by
the press or by the public who may not be experts in
CT. 

The assumptions used in Brenner’s article remain
controversial even among experts in radiation biology.
The underlying data in Brenner’s calculations are
based upon a number of controversial assumptions – for
example, the risk coefficients used by Brenner are
derived from studies of the Japanese citizens who were
exposed to large amounts of radiation during the
A-bomb attacks of Hiroshima and Nagasaki 62 years ago.
These individuals were exposed head to toe to a
mixture of x-ray and particulate radiations, whereas
CT examinations involve only x-rays over a small
fraction of the patient’s body, for example the head
or the abdomen. In addition, the majority of the
A-bomb survivors experienced radiation doses many
times that of modern computed tomography, and the
mathematical methods (called extrapolation) used in
scaling the very high radiation exposures levels down
to the much lower exposure levels typical of partial
body CT examinations remains very controversial.
Indeed, the underlying risk data used by Brenner and
Hall used the most extreme mathematical assumptions –
those which would predict the most harm from CT. The
data from the Japanese bomb survivors is also
consistent with more moderate risk assumptions. 

Another significant flaw in the assumptions used by
Brenner and Hall is that the radiation risks derived
from the Japanese studies are applicable to the
patients receiving CT in the US in 2007. Patients who
require medically indicated CT scans, in the broad
brush of generalities, are sicker than most Americans
and thus have greater health risks and are far
likelier to benefit from the diagnostic information
that the CT examination provides to doctors involved
in their patient care. The population of patients
undergoing CT is also significantly older than the
normal population, and although Brenner and Hall
corrected for age using data derived from the 1945
Japanese population, they did not correct for the many
underlying confounding age dependent variables that
differ between this population and older Americans,
such as the incidence of obesity and diabetes. 

The bottom line is that patients and parents or loved
ones of patients who have had CT scans, or are slated
to have CT examinations in the next days and weeks,
should discuss with their physicians not only the
radiation risks of the CT examination, but the risks
of not having the diagnostic information that CT
provides. Before the invention of CT (in 1972),
exploratory surgery was common practice. CT and other
imaging procedures have virtually eliminated the need
for exploratory surgery, since these technologies
allow doctors to peer inside the patient without the
use of a scalpel. Nobody wants to go back to the days
of exploratory surgery, which has a number of
significant risks including that of bleeding to death,
infection, or debilitating nerve damage. While the
AAPM strongly endorses the Brenner and Hall concerns
that CT should be used only when medically necessary,
we have the steadfast belief that the medical
information gained by medically indicated CT studies
leads to better medical decisions, better patient
care, and a significant improvement in human health. 

David Brenner and Eric Hall are esteemed scientists
and respected experts in radiation risk, and in no way
is this synopsis meant to impeach or undermine their
impressive credentials. Nevertheless, while it is
assumed by many in the lay press that science should
be definitive and consistent, the consequences of the
radiation exposure from CT procedures remain subject
to interpretation of the sparse data that are
available. It is emphasized that the conclusions of
the Brenner article are based on statistics and many
statistical assumptions, they are not based on the
actual observation of somebody dying from having a CT
scan. 

If questions among patients or referring physicians
remain in regards to the radiation risks of CT, they
are encouraged to contact medical physicists who are
employed by their local medical center or academic
radiology department. 

1. DJ Brenner and EJ Hall, Computed Tomography – An
Increasing source of radiation exposure, NEJM 327:22,
2277 (2007). 

Related Links: 

ACR Responds to NEJM Article on Radiation Risk
Associated With CT Scans 

RSNA News Release - Radiologists, Medical Physicists
Working Toward Patient Safety in CT 

+++++++++++++++++++
"Courage is what it takes to stand up and speak, Courage is also what it takes to sit down and listen." -- Sir Winston Churchill

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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