# Childhood CT Scans May Slightly Increase Lifetime Risk of Leukemia and Brain Tumors

 

 

      DynaMed Weekly Update - Volume 7, Issue 24 

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As previously highlighted in a Dynamed Weekly Update in 2010 ([volume 5, issue 2)](http://archive.constantcontact.com/fs028/1102736301344/archive/1102938587539.html), radiation exposure from computed tomography (CT) scans in adults has been associated with increased lifetime cancer risk ([Arch Intern Med 2009 Dec 14;169(22):2071](http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=Abstract&list%5Fuids=20008689&holding=caugamlib)). A new retrospective cohort study has evaluated the risks of leukemia and brain tumors associated with childhood CT scans. Patients in Great Britain who had at least 1 CT scan before the age of 22 years and had no previous cancer diagnosis were assessed for absorbed radiation doses in red bone marrow and brain tissue. A cohort of 178,604 patients was analyzed for incidence of leukemia and a cohort of 176,587 patients was analyzed for brain tumors. Patients were excluded for diagnosis of leukemia within 2 years or brain tumor with 5 years of CT scan to reduce the risk of counting preexisting cancers.

Absorbed radiation dose, measured in milliGrays (mGy) varies with age and scan location. For a 5-year old child receiving a head CT, the typical brain exposure would be about 28 mGy and the estimated red bone marrow dose would be about 9 mGy. A chest CT gives lower doses to both brain tissue and bone marrow. A 15-year old adolescent would typically receive a brain dose of about 44 mGy and a bone marrow dose of 5 mGy from a head CT.

During follow-up of up to 23 years, leukemia was diagnosed in 74 patients (0.04% of cohort) and brain tumors were diagnosed in 135 patients (0.08% of cohort). Increasing radiation dose was associated with increased cancer risk. For each 1 mGy increase in dose the excess relative risk for diagnosis of any leukemia was 0.036 (95% CI 0.005-0.12), and the excess relative risk for any brain tumor was 0.023 (95% CI 0.01-0.049). Compared to cumulative doses< 5 mGy, a cumulative dose of ≥ 30 mGy was associated with increased risk of leukemia (relative risk 3.18, 95% CI 1.46-6.94) and a cumulative dose of 50-74 mGy was associated with increased risk of brain tumor (relative risk 2.82, 95% CI 1.33-6.03).

In terms of absolute risk, these results correspond to an estimate of 1 additional case of leukemia and 1 additional brain tumor over 10 years per 10,000 children having a head CT scan at ≤ 10 years old. Though low, these risks should be considered when weighing the clinical value of a CT scan in a child, especially when other options may exist ([Lancet 2012 Jun 7 early online](http://www.thelancet.com/journals/lancet/article/PIIS0140-6736%2812%2960815-0/fulltext?_eventId=logout)).

For additional information, see the [Acute lymphoblastic leukemia (ALL)](http://search.ebscohost.com/login.aspx?direct=true&db=dme&AN=116388&site=dynamed-live&scope=site), [Myelodysplastic syndrome](http://search.ebscohost.com/login.aspx?direct=true&db=dme&AN=114054&site=dynamed-live&scope=site), and [Brain tumor](http://search.ebscohost.com/login.aspx?direct=true&db=dme&AN=114349&site=dynamed-live&scope=site) topics in DynaMed.