Five to 9 million pediatric CT scans are performed each year in the United States — an eightfold increase since 1980. As the number of scans has grown, so have concerns about radiation exposure in the children undergoing them.
Children are more sensitive to radiation than adults are, and their longer life expectancy provides more opportunity for radiation-associated problems to develop. They are also more likely to experience cumulative radiation damage.
One large study found that a cumulative dose of 50 to 60 mGyo the head — the amount of radiation absorbed from just two or three head CTs — tripled the risk of brain tumors. The same dose to bone marrow tripled the risk of leukemia.
The challenge in emergency medicine is how to weigh the risk of undetected injury against the uncertain harms of radiation exposure.
"It's a really difficult problem," says James L. Homme, M.D., assistant professor of emergency medicine and pediatrics at Mayo Clinic in Rochester, Minn. "We know that radiation is not no risk, but we don't know how to quantify how much risk there actually is from diagnostic imaging. But while people vehemently debate this, the ALARA principle should always be followed."
ALARA, the acronym for "as low as reasonably achievable," is a system for limiting the amount of radiation patients receive. It is based on the tenet that even small amounts of radiation can increase the risk of cancer.
According to the ALARA principle, the benefits of properly performed CT tests should always outweigh the risks for any individual child.
"In pediatric emergencies, if there is a high likelihood of injury that may need intervention, then we don't worry about radiation because the risk of injury is greater," explains Dr. Homme. "But so many patients have a very low risk of injuries that are going to need intervention, yet the tendency is to scan just to be absolutely certain. We have good data to predict when head scans are needed, less on blunt abdominal trauma. But most abdominal injuries are not operative in children anyway, so it's not as imperative to find them."
Dr. Homme says it's important to consider modalities that don't use ionizing radiation, such as ultrasound and in some cases MRI, whenever possible. "There may be some slight sacrifice in sensitivity, but there is also no risk," he points out.
When pediatric CTs are performed, radiologists should adjust parameters for a child's size and weight, scan the smallest possible body area, and use lower mA settings for skeletal and lung imaging. Multiphase exams, which greatly increase the dose of radiation, should be avoided, especially in chest and abdominal imaging.
Dr. Homme says use of pediatric scans ultimately needs assessment on a case-by-case basis, taking into account provider risk tolerance as well as the risk tolerance of parents and patients.
"We must be sensitive to parents' concerns about radiation and be able to address them — whether to allay them when a study is clearly indicated or to factor in risk when a parent or caregiver wants a scan just to be sure," he says. "Wanting to be sure is fine if there is no risk, but when there is risk, you have to have that conversation with the family."
He says he bases his decisions in the ED on what he would want for his own children.
"There has been an astronomical increase in the use of CT scans but no significant increase in great patient outcomes. We're doing more imaging, but that's not necessarily translating into better patient care. Everybody agrees that we're probably doing too much scanning on a population basis. But you can't make that determination with regard to an individual scan without considering all the factors."