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CT Scans Present Higher Risk of Cancer Than Clinicians Realize

SASKATOON, CANADA – Emergency department staff and other healthcare professionals aren’t always aware enough of how diagnostic tools such as computed tomography (CT) scans affect patients’ lifetime malignancy risk, according to a new study.

A Canadian study in the Journal of Medical Imaging and Radiation Sciences was based on a survey of physicians, radiologists, and imaging technologists regarding their beliefs about radiation exposure from CT. Results indicate that, while most respondents recognized an increased risk of cancer from CT, many underestimated the actual radiation dose as well as the dangers of ionizing radiation.

For the study, researchers from the University of Saskatchewan surveyed medical professionals in that area, finding that 73% of physicians, 97% of radiologists, and 76% of technologists correctly identified that there is an increased cancer risk from one abdominal-pelvic CT.

Only 18% of physicians, 28% of radiologists, and 22% of technologists were able to correctly identify the dose in relation to chest X-rays, however. The dose was accurately estimated or overestimated by 48% of physicians, 78% of radiologists, and 63% of technologists, while the rest underestimated the dose level.

"Underestimating radiation dose from a CT scan is more concerning than knowing the exact dose level, particularly when it is a vast underestimation, as this may lead to minimization of the risk estimate when considering a test," explained lead author David Leswick, MD, FRCPC.

The study points out that, measured in millisieverts (mSv), the average radiation dose from an abdominal-pelvic CT is 10 mSv, compared to 0.02 to 0.2 mSv from one chest X-ray, meaning that a radiation dose from a CT scan is best approximated as between the dose from 100-250 chest radiographs.

"Although risk from radiation dose levels in the range of medical imaging procedures is small, it is real as evidenced from atomic bomb survivors and nuclear industry workers showing significantly increased risk of malignancy after exposure to doses in the range of diagnostic CT," Leswick said in a University of Saskatchewan press release. "The risk of fatal malignancy may be as high as 1 in 1,000 for a 10-mSv exposure (approximate dose of an abdomen-pelvis CT). This risk is significant on a population basis, with up to 2% of cancers in the United States population possibly attributable to CT."

Most, 93%, of survey respondents said they were interested in radiation dose feedback when considering ordering a CT scan. Study authors note that automated dose calculation software and radiology information systems can be integrated into electronic ordering, which would give doctors immediate access to information when considering ordering a scan.

The study also uncovered some confusion regarding radiation exposure from magnetic resonance imaging (MRI) and ultrasound, which do not employ ionizing radiation. The survey found that 20% of physicians, 6% of radiologists, and 7% of technologists attributed radiation exposure to MRIs, and 11% of physicians, 0% of radiologists, and 7% of technologists believed that an ultrasound used radiation.

"Belief that ionizing radiation is utilized by ultrasound and MRI is troubling, as it may result in underutilization of these imaging modalities because of unfounded radiation concerns," Leswick.emphasized.