Increased use of pediatric CT poses significant oncogenic risk [Classics Series]

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials

1. Between 1996 and 2010, the use of computed tomographic (CT) imaging increased 2- to 3-fold for children up to 14 years of age, with effective radiation doses per scan varying widely, but ranging up to 69.2 mSv/scan.

2. The highest average radiation doses were delivered by abdominal and pelvic CT scans, with up to a quarter of such scans providing over 20 mSv/scan. A corresponding lifetime attributable risk of solid oncogenesis was estimated at 1 tumor for every 300-390 scans at worst, varying by age, sex, and scan type.

Original Date of Publication: June 2013

Study Rundown: The expanding uses of pediatric imaging have dramatically improved modern diagnostic capabilities. With this expansion has come an increasing concern for the possibility of associated oncogenic risk due to the delivery of ionizing radiation from techniques such as CT. Children are thought to have increased risk of radiation-induced cancers due to their young age, reduced radiation attenuation secondary to smaller body sizes, and the potential for increased radiation doses due to a failure to appropriately alter scanning protocols from an adult to a pediatric paradigm. Previously, Mathews et al. estimated that the incidence of cancers due to childhood CT exposure was 24% higher in irradiated subjects than controls, with risk increases proportional to dose, and inversely proportional to age at exposure. The current study sought to retrospectively examine trends in CT use, including doses delivered to children during individual CT scans, and project an attributable carcinogenic risk of such scans in an effort to offer targeted dose reduction strategies. During the study period from 1996 to 2010, the authors found that CT use had sharply increased, doubling for children under age 5 and tripling for those aged 5-14 before peaking around 2007 and downtrending thereafter. Effective single scan doses were highly variable across sites and scanners, ranging from 0.03 to 69.2 mSv/scan, with up to a quarter of children receiving doses greater than 20 mSv/scan. The most frequently ordered scans were of the abdomen and pelvis, which also carried the highest average radiation dose and corresponding oncogenic risk, estimated at 25.8 to 33.9 cases per 10 000 scans for girls, and 13.1 to 14.8 cases per 10 000 for boys. Lifetime attributable solid cancer and leukemia risks were calculated based on individual organ dosimetry and were highest for girls and younger children. These data suggested that nearly 5000 future cancers could be attributed to pediatric CT use per year in the United States, and that a reduction of the highest quartile of doses could prevent over two fifths of such cancers.

Click to read the study in JAMA

In-Depth [retrospective cohort]: Between 1996 and 2010, this study retrospectively observed CT use patterns in children aged 15 or younger at six large health maintenance organizations (HMOs) within the HMO Research Network across the United States. Roughly 150 000 to 370 000 children were included in the study per year (50% female, 29% under 5 years of age.) CT use increased steadily between 1996 and 2005, peaking at a doubling of scans for children under age 5 and a tripling of scans for children aged 5 to 14. From 2007 onward, CT utilization trended down. The most commonly ordered scans were of the head, abdomen/pelvis, thorax and spine, respectively, with abdominal/pelvic scans seeing the greatest increase in use. Effective radiation doses, on a per organ basis, were calculated using age- and sex-specific computational anatomy phantoms and the abstracted study parameters of 744 randomly selected individual scans. From these data, lifetime attributable risks of cancer were projected using multiple previously published risk models based upon data from the Life Span Study of Japanese atomic bomb survivors. Solid tumor risks increased with earlier ages at exposure, increased dose, and female gender. Using abdomen/pelvis CTs as the highest risk index scenario, 1 radiation-induced tumor was predicted for every 300-390 and 670-760 scans for girls and boys, respectively.) Leukemia risks were highest for head CTs in children under age 5, at 1 case of leukemia per 5250 head CTs performed in this age group. Projection of these findings to the United States at large suggested that each year, pediatric CT imaging could conservatively be attributable to the development of 4870 future cancers. Reductions in delivered doses or scan frequency through standardized pediatric dose reduction protocols, increased use of alternative imaging modalities such as ultrasound or magnetic resonance imaging, and implementation of stricter appropriateness guidelines to reduce unnecessary scans could significantly reduce oncogenic risks. More specifically, a reduction of the highest 25% of doses delivered per scan to the median dose could prevent 43% of attributable tumors, while a 33% reduction in CTs performed would reduce cancers by an equal proportion.

Miglioretti DL, Johnson E, Williams A, Greenlee RT, Weinman S, Solberg LI, et al. The use of computed tomography in pediatrics and the associated radiation exposure and estimated cancer risk. Journal of the American Medical Association. 2013 Jun 10;167(8):700–07.

Mathews JD, Forsythe AV, Brady Z, Butler MW, Goergen SK, Byrnes GB, et al. Cancer risk in 680 000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ. 2013 May 21;346:f2360.

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