Dr. Craft said that kids with the highest exposures—at least 30 mGy—had a risk of developing cancer that is three to five times greater than those with the lowest exposure—less than 5 mGy. “In absolute numbers, the risk of leukemia went from 1 in 2,000 to 1 in 300 to 400,” he said. “It’s still incredibly rare. But it’s still clearly an increased risk.”
Explore this issue:September 2012
Obviously, the study was retrospective and observational, not a clinical trial. Some scientists point to other potential weaknesses, such as the lack of a no-exposure control group and no data as to why the CT scans were done. Also, said Robin Cotton, MD, director of otolaryngology at Cincinnati Children’s Hospital Medical Center, “Doses have been going down, down, down.”
Some have maintained that nothing untoward happens with the much lower doses of radiation received in medical imaging, said Mike Hanley, MD, an attending radiologist at the University of Virginia School of Medicine in Charlottesville. At the very least, the Lancet study, which used data from medical records in the UK, suggests that there’s some risk at lower levels of exposure, he said.
The risk is real but very tiny—at least for a single scan. “I don’t think much about one CT scan,” Dr. Cotton said. “But I do think about two CT scans.”
On the plus side, sinus CT scans deliver relatively low radiation doses (typically less than 1 mSv) compared with chest (6-7 mSv) or coronary CT scans (12-16 mSv). But that shouldn’t give otolaryngologists license to scan without pause. Of course CT scans should be administered only when warranted, Dr. Craft said. Still, “people have got to think twice and thrice. Each CT scan adds to risk,” he added.
The benefits of CT scans for diagnosing sinus disease are well known to ENT surgeons. By the time patients are referred, they probably have already been through some diagnostic tests and medical treatments. Surgeons use the CT scan to provide a quick, definitive answer and to determine who might benefit from surgery, said Terence Davidson MD, an otolaryngologist/ENT surgeon at the University of California San Diego School of Medicine. The test is also used to provide a roadmap for sinus surgery, said Dr. Cotton.
Physician Knowledge Sometimes Lacking
There are no clinical practice guidelines regarding when to use sinus CT scans in adults or kids. The burden is on physicians to understand the radiation exposure they’re giving, as well as associated risks. Patients are asking for this information more frequently, in part because of the news generated by the Lancet study, as well as a recent study about dental X-rays and brain tumors (Cancer. 10 April 2012, doi: 10.1002/cncr.26625).