More than a million European children undergo a CT scan each year. Ionizing radiation at moderate (> 100 mGy) to high (> 1 Gy) doses is a recognized risk factor for malignant hematopathies. The risk associated with exposure to low doses (< 100 mGy), typically delivered during a CT scan in children or adolescents, is unknown.
Previous studies assessed the risk for malignant hematopathies related to ionizing radiation from CT scans in young patients. Some showed an increased risk for leukemia with repeated scans, but confounding factors resulted in a lack of statistical power or biases in some cases. The EPI-CT study, coordinated by the International Agency for Research on Cancer, aimed to evaluate the cancer risk among children and adolescents after exposure to low doses of ionizing radiation during CT scans.
A European Cohort
A recent article presents an assessment of observed malignant hematopathies following CT scan. The authors followed a multinational European cohort of 948,174 patients who had a CT scan before age 22 years. Ionizing radiation doses to the bone marrow were evaluated based on the scanned body region, patient characteristics, scan year, and the technical parameters of the machine. The analysis involved 876,771 patients who underwent 1,331,896 scans (an average of 1.52 per patient) and were followed for at least 2 years after the first scan.
In total, 790 malignant hematopathies were diagnosed, including 578 lymphoid hematopathies and 203 myeloid hematopathies and acute leukemias. The average follow-up period was 7.8 years. At the time of diagnosis, 51% of patients were under the age of 20 years, and 88.5% were under the age of 30 years. There was an association between cumulative dose and the observed malignant hematopathy, with an observed rate of 1.96 per 100 mGy (790 cases).
This rate corresponds to a 16% increased rate per scan (for a dose observed per scan of 8 mGy). A higher rate for any type of malignant hematopathy was observed for doses > 10 mGy, with an observed rate of 2.66 for doses > 50 mGy, compared with doses < 5 mGy.
The rate of malignant hematopathy increased with older age at the time of radiation exposure, particularly for lymphoid observations. The rate in the 5- to 9-year age group and the > 10-year age group was, respectively, two times and three to four times higher than that in the < 5-year age group. The rate decreased over time, with the highest observed rate between 2 and 5 years after ionizing radiation exposure and the lowest after 10 years.
CT Scans Must Be Warranted
This study, which involved nearly a million patients, has higher statistical power than previous studies, despite missing or approximate data (including that related to actually delivered doses). An association was shown between cumulative dose to the bone marrow and the risk of developing malignant hematopathy, both lymphoid and myeloid, with an increased risk even at low doses (10-15 mGy).
The results suggest that for every 10,000 children examined today (with a dose per scan of 8 mGy), 1-2 could develop a radiation-related malignant hematopathy in the next 12 years (1.4 cases). This study confirms the higher risk for cancer at low radiation doses and emphasizes the importance of justifying each pediatric CT scan and optimizing delivered doses. It is important to recall that an MRI or ultrasound can sometimes be an adequate substitute for a CT scan.
This article was translated from JIM , which is part of the Medscape Professional Network. A version of this article appeared on Medscape.com .