A new study is evaluating relationships between cumulative radiation exposure related to medical imaging and later cancer risk. A description of the study’s methods and cohorts was recently presented in the journal Cancer Causes & Control.
“While computed tomography (CT) has improved diagnostic capabilities, it has also increased patient exposure to ionizing radiation, a known carcinogen,” the study investigators explained in their report. Additionally, several other types of medical imaging tests involve ionizing radiation.
The study is the retrospective, longitudinal Risk of Pediatric and Adolescent Cancer Associated With Medical Imaging (RIC) Study, evaluating effects of fetal and childhood medical imaging-based radiation exposures. It included patients from 6 locations in the US and 1 site in Ontario, Canada, over the years of 1995 through 2017. There was a fetal-exposure cohort and a childhood-exposure cohort.
Patient histories of imaging utilization and cancer histories were used to evaluate associations between radiation exposure and cancer risk. Estimates of radiation dosages were derived based on type of test and associated protocol information, with tests including CT, radiography, fluoroscopy, angiography, and nuclear medicine-based methods.
There were 3,474,000 children in the fetal-exposure cohort, with median ages at end of follow-up of 11 years for the US patients and 10 years for the Canadian patients. In the fetal-exposure cohort there were 6606 cancers diagnosed across 37,659,582 person-years. Of these cancers, 2,394 were leukemias. In the fetal-exposure cohort there 10,950 all-cause deaths were identified, which reflected cumulative incidence rates of 429 per 100,000 children in the US and of 509 per 100,000 children in Ontario.
In the fetal-exposure cohort, the percentages of children having had in utero exposures to radiation from medical imaging included 0.5% exposed through CT imaging, 4.0% exposed through radiography exams, 0.4% exposed through fluoroscopy exams, 0.04% exposed through angiography exams, and 0.2% exposed through nuclear medicine exams.
The childhood-exposure cohort consisted of 3,724,632, with median ages at the end of follow-up of 5 years in US patients and 11 years in the Canadian patients. In this cohort 6,358 cancers were identified across 36,190,027 person-years. Of these cancers, 2,372 had been leukemias. All-cause deaths totaled 4,915 in patients of the childhood-exposure cohort, reflecting cumulative incidence rates of 344 per 100,000 children in the US and 324 per 100,000 in children in Ontario.
In the childhood-exposure cohort, the percentages of children exposed to radiation with medical imaging included 5.9% exposed through CT exams, 61.1% exposed through radiography exams, 6.0% exposed through fluoroscopy exams, 0.4% exposed through angiography exams, and 1.5% exposed through nuclear medicine exams.
“Our study is one of the largest and most contemporary to examine risk of childhood cancers associated with medical radiation from in utero and childhood exposure over a 22-year span comparing an exposed group to an unexposed group,” the study investigators wrote in their report. They indicated the primary analyses of the RIC Study are forthcoming.
Kwan ML, Miglioretti DL, Bowles EJA, et al. Quantifying cancer risk from exposures to medical imaging in the Risk of Pediatric and Adolescent Cancer Associated with Medical Imaging (RIC) Study: research methods and cohort profile. Cancer Causes Control. Published online February 2, 2022. doi:10.1007/s10552-022-01556-z