Image: CC/rosiescancerfund
Computed tomography (CT) imaging is a quick and easily accessible diagnostic tool, and its use has increased over the past decade. Compared to traditional radiography, however, CT imaging exposes patients to much higher radiation doses, and there is uncertainty regarding how radiation exposure from CT imaging will impact a patient’s risk of developing cancer.
A study recently published in The Lancet explored the risk of leukemia and brain tumors in patients who had CT scans as children. This retrospective cohort study involved 178,604 individuals in its leukemia analysis and 176,587 individuals in its brain tumour analysis. This study was conducted in Great Britain, and data were accessed from the National Health Service Central Registry.
The risk of leukemia was positively associated with the estimated dose of radiation delivered to the red bone marrow by CT scans (p=0.0097), as the relative risk (RR) in patients receiving 30 mGy compared to patients receiving doses of less than 5 mGy was 3.18 (95% CI 1.46-6.94). A similar association was demonstrated between the risk of brain tumors and the estimated doses of radiation from CT scans to brain tissue (p<0.0001). The relative risk of brain tumours in patients receiving 50-74 mGy was 2.82 (95% CI 1.33-6.03) when compared to patients receiving less than 5 mGy.
While previous studies have described elevated risk of cancer after radiation exposure, this is the first cohort study to assess the risk of cancer after exposure to radiation from CT scans. Interestingly, the findings in this study are quite consistent with those of the Life Span Study of Japanese atomic bomb survivors, as the excess relative risk (ERR) per mGy in both studies are quite similar for both leukaemia and brain tumours. Thus, with increasing use of CT imaging in the childhood population, it is crucial to consider the increased risk of developing cancer as a result of higher radiation exposure. Note the typical limitations of retrospective cohorts and the fact that the absolute increases in these cancers, while very real, were still small.
Click to read the report in The Lancet.
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