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.
- 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, "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 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).http://www.ajronline.org/cgi/content/full/176/2/303
- Imaginis provides in-depth information on CT scanning
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.
