A certain segment of patients is prone to undergoing dozens of CT scans, potentially increasing their chance of harm from radiation and contrast agents.
Wanting to better understand this population, a group of researchers from one Dutch institution analyzed data from nearly 274,000 scans, interpreted by radiologists over a 10-year period. While the amount of computed tomography super users was relatively low—at just 0.06%—radiation levels were noteworthy, scientists reported Thursday in the European Journal of Radiology.
“These numbers are non-negligible, and should raise awareness among oncologists, surgeons and radiologists who take care of these patients,” wrote Thomas Kwee, with the Department of Radiology at the University of Groningen, Netherlands, and colleagues.
“Awareness in clinical practice may be increased by implementing software for automatized individual patient dose tracking, and this information should be available to both the referring physician and the radiologist in the electronic patient files,” the team added.
All told, Kwee et al. estimated that 56 patients in the study population received 40 or more CT scans apiece during the study period, out of almost 101,000 individuals. Those super users had a median age of 58 and underwent 47 scans over the course of the decade ending in 2017.
Cancer was the driver of all such exams, with lung (18%), melanoma (16%) and colon (14%) the top drivers. For all but one patient out of the 56, the disease had metastasized. Twenty-six patients received chemo (46%), 35 had radiation therapy (62%) and 38 received targeted therapy (68%), among other treatments. And CT super users had a mean survival rate of about six and a half years.
Kwee and colleagues reported an estimated overall radiation-induced lifetime attributable risk of cancer incidence of 1%, and mortality due to multiple repeated CT scans at 0.68%. And extremes reached as high as 2.36% and 1.37%, respectively.
Mean cumulative volume of IV-injected contrast agents was 2,339 milliliters—a finding they say requires further investigation. More than 5% developed severely decreased kidney function, though this could have also been fueled by numerous other factors, authors wrote.
While the study has numerous limitations—including setting an arbitrary number of 40 scans for super users—the key takeaway is to use caution when treating such patients, the team concluded. And where possible, consider radiation-free, whole-body MRI as an alternative.
“The presented data re-emphasize the need to carefully consider the need of each CT scan, and to exercise restraint when CT results are unlikely to have a clinical benefit or management consequences,” Kwee and colleagues concluded.