Jan. 22, 2001 -- When a child has to undergo an imaging study, such as an X-ray or a CT scan, it makes sense to keep the radiation dose as low as possible. However, healthcare professionals don't have a lot of information to go on to help them know exactly how to adjust the radiation dose to compensate for a child's smaller size.
Researchers in the latest issue of the American Journal of Roentgenology investigated whether CT scan could be made even safer for children by adjusting the radiation dose to their weight. They found that this goal was achievable without sacrificing accuracy in diagnosis, and they are calling for new guidelines for CT scans in children.
CT scan is a technique similar to X-ray for examining the body's internal structures. However, it requires a larger dose of radiation in order to generate an image. The imaging technique is widely used for a variety of pediatric situations, such as the diagnosis of appendicitis or kidney stones.
Although CTs account for only 4% of medical X-rays, they contribute 40% of the total collective radiation dose. Because children have many years ahead of them in which to be exposed to radiation, the higher dose used in CT scans is somewhat of a concern in younger patients. Doctors want to limit the radiation exposure as much as possible.
"The risks [from CT scan] are highly outweighed by the benefits," lead study author Lane F. Donnelly, MD, tells WebMD. "The radiation dose of CT is minimal, but it's not completely zero. We want to take a good thing -- low doses of radiation associated with CTs -- and make it better by making the dose lower still." Donnelly is a staff radiologist at Children's Hospital Medical Center in Cincinnati, where he is an associate professor of radiology and pediatrics at the University of Cincinnati.
In their article, Donnelly and his colleagues report on their experiences with minimal radiation doses for pediatric CTs. They found that they could reduce the overall radiation dose using two techniques: by reducing the tube current, a measurement of radiation, and by increasing the pitch, the time an X-ray beam needs to scan an area. They reduced the tube current according to the child's weight. And, by doubling the pitch, they decreased the radiation dose by half.
"We are not aware of any cases in which a diagnosis, that was not detected on our reduced dose CT, has become evident at a later time," the authors write. "In addition, we have not had to repeat studies ... because of poor technical quality."
The researchers suggest that another way to minimize pediatric CT-related radiation doses is to eliminate inappropriate CT use. They encourage clinicians to use other modalities such as ultrasound and magnetic resonance imaging (MRI), both of which use less radiation, when possible. Also, if a procedure requires the use of an injected dye, physicians can skip the step of doing an image before the dye is used and only do the CT after the dye is injected.
According to one expert, this article may help parents communicate with radiology technicians to make sure that children who need a CT scan get the lowest possible radiation dose.
"The guidelines [in the article] are reasonable guidelines to follow," says Robert Lavey, MD, head of the radiation oncology program at Children's Hospital of Los Angeles, Calif., who spoke with WebMD about the research. "Radiologists can use the guidelines as a starting point and make adjustments as they find necessary for their scanners. ... The [parent] bringing his or her child for a scan can ask the technician whether the tube current and pitch have been adjusted for the child's size prior to obtaining the scan. In this way, a scan can be performed, and yet parents can do their best to protect their child."
"Although we want to lower the CT-associated radiation dose, parents should not be worried if their children need to have CTs," Donnelly tells WebMD. "This is a helpful medical tool, and often it's the best tool to get the information we need to care for children."