Monday, June 17, 2013

Pediatric CT Scans Raise Future Cancer Risk

Ricki Lewis, PhD

Jun 10, 2013
The number of computed tomography (CT) scans of the head, abdomen/pelvis, chest, or spine performed on children younger than 14 years has risen dramatically since 1996, elevating radiation-induced cancer risk, according to studypublished online June 10 in JAMA Pediatrics.
Children are particularly sensitive to radiation, and their age allows many years for cancers to develop. CT scans deliver 100 to 500 times higher doses of ionizing radiation than conventional X-rays, and several studies have linked these doses to elevated cancer risk.
Diana L. Miglioretti, PhD, from the University of California, Davis, and colleagues conducted a retrospective observational study to quantify trends in pediatric CT use in 6 diverse US healthcare systems. They evaluated 4,857,736 child-years and calculated radiation doses for a random sample of 744 scans. The body regions studied account for 95% of pediatric CT scans.
Outcomes were rates of CT use, doses, and projected lifetime attributable risks of cancer.
From 1996 through 2005, CT use doubled for children younger than 5 years and tripled for children aged 5 to 14 years. Rates stabilized in 2006 and 2007 and have declined since then.
Effective doses varied widely, from 0.03 to 69.2 mSv per scan. From 14% to 25% of abdomen/pelvis scans received an effective dose of 20 mSv or higher, as did between 6% and 14% of spine scans and from 3% to 8% of chest scans.
Younger patients and girls face higher projected lifetime attributable risk for solid cancers than older patients and boys. The researchers calculated that for girls, 300 to 390 abdomen/pelvis scans would cause a single radiation-induced solid cancer, whereas 670 to 760 of such scans would do so for boys. Risks were highest for CT scans to the abdomen/pelvis or spine.
Leukemia risk was highest for head CTs on young children. The risk decreased from 1.9 cases per 10,000 scans for children younger than 5 years to 0.5 cases per 10,000 scans for children aged 10 to 14 years. Among the older children, leukemia risk was highest for abdomen/pelvis scans (1.0 cases per 10,000 scans).
Theoretically, the approximately 4 million pediatric CT scans performed in the United States each year to the specified body parts will cause approximately 4870 cancers. The researchers estimate that lowering the highest 25% of doses to the median could prevent 43% of the projected radiation-induced malignancies, but reducing the highest 50% of doses would only prevent an additional 8% of cancers.
The investigators call for further research to identify situations in which CT scans of children improve health outcomes and are the most effective diagnostic method. They conclude, "Implementation of...readily available dose-reduction strategies, combined with the elimination of unnecessary imaging, could dramatically reduce future radiation-induced cancers from CT use in pediatrics."
A limitation is that the assessment may have underestimated cancer risk projections because the protocol counted some multiple scans performed on a single day as 1 scan and considered only cancers with published predictive models.
This study was supported by the Cancer Research Network Across Health Care Systems and the National Cancer Institute. The authors have disclosed no relevant financial relationships.
JAMA Pediatr. Published online June 10, 2013. Abstract

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