Australian news, and some related international items

Australian study shows increase in cancer among children who had CT scans

CT Scans May Increase Cancer Risk in Children, Adolescents Larry Hand May 23, 2013      Children and adolescents who undergo computed tomography (CT) scans may be at greater risk of developing cancer compared with individuals who do not, according to a study published online May 21 in the British Medical Journal. However, the absolute risk for all cancers is relatively low.John D. Mathews, MBBS, MD, PhD, DSc Hon, DMedSc Hon, professor of epidemiology at the School of Population and Global Health, University of Melbourne, Carlton, Victoria, Australia, and colleagues analyzed the records of children and adolescents aged 0 to 19 years who were included in the Australian Medicare database between January 1, 1985, and December 31, 2005. They followed the study population through electronic linkage to the Australian Cancer Database and the National Death Index through December 31, 2007.

Of a total of 10.9 million people in the overall cohort, 680,211 individuals had been exposed to low-dose ionizing radiation through CT, and 18% of those individuals had had more than a single CT scan. The researchers based their main analysis on a 1-year lag between CT scan and cancer diagnosis to minimize the possibility that the scan might be part of a cancer diagnostic procedure. They also considered 5- and 10-year lag periods in further analyses.

During a mean follow-up period of 9.5 years for the exposed group and 17.3 years for the unexposed group, 3150 exposed individuals and 57,524 unexposed participants were diagnosed with a cancer. Overall cancer incidence for the 1-year lag was 24% higher in the exposed group after adjusting for age, sex, and year of birth (incidence rate ratio [IRR], 1.24; 95% confidence interval [CI], 1.20 – 1.29; P< .001). Incidence remained higher in the exposed group for 5- and 10-year lags, but proportional increases were smaller.

Brain cancer had the highest IRR, at almost twice the overall rate for individuals who had a brain CT scan (IRR, 2.44; 95% CI, 2.12 – 2.81). Excess brain cancers for the exposed individuals who had brain scans were calculated at 122.7, with an excess incidence rate of 2.97 (95% CI, 2.28 – 3.66). However, the increase in IRR was maintained for all cancers after an analysis excluding brain cancer.

IRRs were highest for CT exposures in children younger than 5 years but decreased with increasing age at first exposure (P = .001 trend for brain cancer trend; P < .001 trend for all cancers).

The researchers calculated the absolute incidence rate for all cancers combined at 9.38 per 100,000, which amounts to 608.4 excess cancers for the exposed group, or 1 excess cancer in every 1800 CT scans.

“[T]he inference that CT scans cause most of the excess cancer in exposed people cannot be conclusively proven,” but is supported by several observations such as the ones above, the researchers write.

In an accompanying editorial, Aaron Sodickson, MD, PhD, section chief of emergency radiology and medical director of computed tomography at Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, writes that, in perspective, “The authors found an overall risk of about 0.125 cancers per Sievert [of exposure]…. This would equate to roughly one excess cancer per 4000 head CTs at the more typical doses in use with current day technology.”

May 25, 2013 - Posted by | AUSTRALIA - NATIONAL, health

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