Computed Tomography (CT) scans are an increasingly used
X-ray-based tool for providing a three-dimensional view
of a particular organ or tissue. The value of CT scanning
to diagnose injury, cancer and other health problems is
undisputed. But are these scans being used too frequently,
in some cases unnecessarily? What are the health consequences
of having too many CT scans over the course of a person's
In a Nov. 29, 2007 article in The New England Journal
of Medicine, David J. Brenner, Ph.D., and Eric J. Hall,
Ph.D., from the Center for Radiological Research at Columbia
University Medical Center, argue that the potential carcinogenic
effects from using CT scans may be underestimated or overlooked.
This is of particular concern, because perhaps one-third
of all CT scans performed in the United States may not
be medically necessary, the radiation researchers say.
It is estimated that more than 62 million CT scans per
year are currently given in the United States, compared
to three million 1980. Because CT scans result in a far
larger radiation exposure compared with conventional plain-film
X-ray, this has resulted in a marked increase in the average
personal radiation exposure in the United States, which
has about doubled since 1980, largely because of the increased
It used to be widely believed that all radiological examinations
were essentially harmless, because of the small amounts
of radiation involved, but Drs. Brenner and Hall show
that this is unlikely to be true for CT scans. In particular,
Japanese atomic bomb survivors who were about two miles
away from the explosions, actually received radiation
doses quite similar to those from a CT scan.
Sixty years of study of these survivors have provided
direct evidence that there will be an increased individual
cancer risk, though small, for those who have this same
dose of radiation from CT scans. Although the individual
risk is small, the large number of CT scans currently
being given may result in a future public health problem.
In particular, Drs. Brenner and Hall suggest that, in
a few decades, about 1½ to 2 percent of all cancers
in the United States may be due to the radiation from
CT scans being done now.
Defensive Medicine Leads to Overuse
Drs. Brenner and Hall suggest that the rapid increase
in CT usage represents a potential public health problem
in the United States that should be proactively addressed.
This is particularly important for children, who are more
sensitive than adults to radiation exposure. The issue
arises, for example, when CT scans are requested in the
context of so-called "defensive" medicine, or
when scans are repeated as a patient passes through different
parts of the medical system.
Compounding the issue, surveys suggest that the majority
of radiologists and emergency-room physicians may not
appreciate that CT scans are likely to increase the lifetime
risk of cancer. Ultimately, the health care system, the
doctor, and the patient (who can perhaps best track of
the number of CT scans performed when dealing with multiple
doctors) may have to share the burden of monitoring the
appropriate dosage and number of scans.
Drs. Brenner and Hall suggest three strategies for proactively
addressing the potential increased radiation risks associated
with CT scans:
- Reduce the CT-related radiation dose in individual
- Replace CT use, when appropriate, with other options
that have no radiation risk, such as ultrasound or magnetic
resonance imaging (MRI).
- Decrease the total number of CT scans prescribed.
Drs. Brenner and Hall suggest in their paper's conclusion
that these strategies could potentially keep 20 million
adults and, crucially, more than one million children
annually from being irradiated unnecessarily. They stress,
however, that in the majority of individual cases, the
benefits associated with a correct diagnosis through CT
will far outweigh the individual risk.