| Radiation doses from computed
tomography (CT) scans are often higher than needed and may contribute to cancer later
in life, according to two new studies published in the American Journal of
Roentgenology. CT scans (also called CAT scans) use digital computers and rotating
x-ray devices to create detailed cross sectional images of organs and body parts. While CT
scans can be very beneficial in detecting disease, researchers have found that many
centers use the same CT settings on children as they do on adults, possibly exposing
children to radiation levels approximately five times higher than necessary to obtain a
quality image. In a study,
conducted by Lane Donnelly, MD, a radiologist from the Children’s Medical Center in
Cincinnati, and his colleagues, the researchers found that the technical components of CT
scans that influence radiation exposure, such as the x-ray tube current, may be set
unnecessarily high at many centers. According to the researchers, the protocols used on
many children are default settings typically intended for adult use. Since children are
much smaller than adults, lower x-ray doses can be used to create suitable images.
CT scans account for approximately 4%
of medical imaging exams; however, research shows that CT scans contribute to 40% of the
total amount of radiation received from diagnostic tests. While Dr. Donnelly and his
colleagues emphasize that the risk from CT radiation exposure is minimal, higher radiation
doses can increase the lifetime risk of cancer in children. "Of the approximately
600,000 abdominal and head CT examinations annually performed in children under the age of
15 years, a rough estimate is that 500 (approximately 1/10th of a percent) of
these individuals might ultimately die from cancer attributable to the CT radiation,"
wrote David Brenner of the Center for Radiological Research at Columbia University and his
colleagues, who performed a study which examined the risks of radiation-induced fatal
cancer from pediatric CT.
The number of CT scans performed in
recent years has also risen dramatically, further creating the need for minimizing
radiation exposure during the test. At the Cincinnati Children’s Medical Center and
many other children’s hospitals, the radiation dose for pediatric CT scan is set
based on the patient’s weight. These adjusted doses are significantly lower than
those used in the past, yet they still produce high quality images.
Unlike other medical imaging exams,
such as conventional x-ray imaging, CT has the ability to image
a combination of soft tissue, bone, and blood vessels. The exam can be very useful in
providing diagnostic information on several areas of the body, including:
- the brain, vessels of the brain, eyes,
inner ear, sinuses
- the neck, shoulders, cervical spine and
blood vessels of the neck
- the chest, heart, aorta, lungs,
mediastinum
- the thoracic and lumbar spine
- the upper abdomen, liver, kidney,
spleen, pancreas and other abdominal vessels
- the pelvis and hips, male and female
reproductive system, bladder, and GI tract
- the skeletal system including bones of
the hands, feet, ankles, legs and arms, and jaws
In most cases, the benefits of finding
disease with a CT scan outweigh the risks of x-ray radiation exposure and/or injections of
imaging contrast and use of sedatives during the scan.
To ensure that their child is receiving
a safe and necessary CT scan, parents may wish to:
- Ask whether the scanning protocol has
been optimized for the child’s weight and body type (this is especially important if
the CT scan is not performed at a children’s center).
- Make sure the CT scan is absolutely
necessary, especially if multiple CT scans are performed.
It is important that radiologists and
radiologic technologists subscribe to the principle of "As Low as Reasonably
Achievable" (ALARA) or "As Low as Reasonably Possible" (ALARP). In essence,
the ALARA/ALARP principle emphasizes using as little radiation as possible in order to
achieve a needed diagnostic result. This can be accomplished by various means including
controlling: how many x-ray exams are ordered, the type of x-ray exam ordered, how often
the exam is performed, performing the exam as accurately as possible to avoid repeat
x-rays, and using the lowest x-ray dose possible to achieve the needed diagnostic result.
In general, newer systems are more
sensitive than older CT systems and may acquire a suitable image using a lower x-ray dose.
CT scanner manufacturers continue to work with radiologists to create technology and
protocols to acquire high quality CT images at the lowest possible dose.
Additional Resources and References
- The study, "Helical CT of the Body:
Are Settings Adjusted for Pediatric Patients?" is published in the February 2001
issue of the American Journal of Roentgenology (Vol. 176, Issue 2). The study is
available online at http://www.ajronline.org/cgi/content/full/176/2/297
- The study, "Estimated Risks of
Radiation-Induced Fatal Cancer from Pediatric CT," is published in the February 2001
issue of the American Journal of Roentgenology (Vol. 176, Issue 2). The study is
available online at http://www.ajronline.org/cgi/content/full/176/2/289
- The perspective report, "Minimizing
Radiation Dose for Pediatric Body Applications of Single-Detector Helical CT: Strategies
at a Large Children's Hospital," is published in the February 2001 issue of the American
Journal of Roentgenology (Vol. 176, Issue 2). The report is available online at http://www.ajronline.org/cgi/content/full/176/2/303
- Imaginis provides in-depth information
on CT scanning at http://www.imaginis.com/ct-scan/
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