An international clinical trial across 100 imaging facilities involving nearly 1 million CT (computed tomography) scans showed that radiation doses could significantly – and safely – be lowered to reduce cancer risk.
The randomized, multicenter trial assessed various approaches to reduce radiation doses for CT scans. The researchers, led by UC San Francisco investigators, found that detailed feedback and sharing of best practices led to significant reductions in the proportion of high-dose scans with no resulting drop in physicians’ satisfaction with image quality. For the body regions where doses tend to be highest, high-dose scans were reduced by as much as 58 percent.
When higher-than-needed doses are used, there’s higher cancer risk without any benefit in improved diagnoses. Reducing CT dosage, as found in this study, could potentially prevent 6,000 cancers a year in the United States alone, said the authors.
The study publishes March 2, 2020, in JAMA Internal Medicine.
“In medical imaging, there is often a tradeoff between radiation doses and image quality,” said lead author Rebecca Smith-Bindman, MD, a UCSF professor of Radiology, Epidemiology and Biostatistics, and a member of the Philip R. Lee Institute for Health Policy Studies. “If doses are too low, this can potentially reduce imaging quality. While it is widely understood that the doses we use for CT are too high, radiologists have been hesitant to lower the doses for fear it will lead to medical errors. Until now, there haven’t been any large studies on whether it’s possible to reduce CT doses while maintaining high image quality.
“We found that CT radiation doses can be significantly reduced through simple, inexpensive interventions without reducing radiologist satisfaction with image quality,” said Smith-Bindman. “We were very excited by these results. High-radiation exposures are almost always unnecessary, so even a small reduction in percentages of high-dose exams is clinically meaningful. Based on the 85 million CT scans that are performed in the U.S. every year, if all imaging facilities performed even 1 percent fewer high-dose CT exams, 212,500 people would avoid receiving a high CT dose annually. This would result in many fewer cancers being caused by the radiation from those exams.”
The use of ionizing radiation in medical imaging has more than doubled over the last three decades, primarily from increased use of CT scans, which deliver radiation doses far higher than conventional radiographs (like chest X-rays or bone X-rays commonly used to diagnose fractures). Ionizing radiation is a known carcinogen, and it’s estimated that 2 percent to 5 percent of all cancers in the U.S. are caused by medical imaging radiation exposure. Children exposed to CT have higher risk of leukemia and brain cancer, and adults have a higher risk of all cancers, especially leukemia, breast cancer and liver cancer.
Despite the established risks, CT doses are often higher than needed for diagnosis, and they also vary considerably across medical imaging facilities. As a result, optimizing CT doses – without affecting diagnostic accuracy – is important and has been identified as a quality and safety issue by oversight organizations and government programs. The goal of this oversight is to encourage appropriate radiation doses – not the lowest possible but the lowest needed to provide clinical answers. But few dose-reducing approaches have been widely tested in randomized controlled trials.