Question

• Eight-year old boy presents to the ED with presumed ventriculo-peritoneal shunt malfunction requires a head CT. Does the ionizing radiation from the CT examination increase the risk of cancer in this patient?

Clinical Bottom Lines

1. Best available risk estimates suggest that pediatric CT will result in significantly increased lifetime radiation risk over adult CT.¹
2. Rapid increase in lifetime cancer risk occurs with decreasing age at exposure to CT.
3. The estimated cancer risk for abdominal CT is significantly greater than that of head CT, because of the larger combined mortality risk (per unit dose) for exposure of the digestive organs relative to exposure of the brain and to thyroid.
4. Karlsson et al have shown that there is a dose-response relationship between absorbed dose in the brain and the subsequent risk of developing an intracranial tumor and that the risk is higher among infants exposed at younger ages.²
5. Studies have suggested that a technique with significant reduction in exposure could be adopted for pediatric CT exams without significant loss of information.³
6. More needs to be done regarding dose reduction by reducing number of CT scans or decreasing radiation dose with each scan.
   

Summary of Key Evidence

1. Although CT exams of patients less than 15 years old contribute to only 4% of all CTs performed, this group is estimated to contribute approximately to 20% of the total potential cancer mortality.¹
2. Lifetime cancer mortality risk attributable to the radiation exposure from a single abdominal CT in a 1-year-old child is approximately one in 550 and approximately one in 1500 for a head CT.
3. In the US each year, at least 600,000 abdominal and head CT exams are performed on children less than 15. The authors estimate that approximately 500 will ultimately die from a cancer attributable to CT radiation.
4. For the approximately 600,000 children less than 15 years old who are estimated to undergo CT each year in the US, approximately 140,000 will ultimately die of cancer. Thus, the estimated 500 CT-related deaths for this population represents only a 0.35% increase over background.
   

Additional Comments

• It was estimated that there was a 600% increase in all CT examinations for the decade spanning the mid 1980s to mid 1990s.⁵
• It is estimated that 4% of diagnostic radiology procedures are CT exams, but their contribution to the collective dose is 40%.¹
• Larger attributable lifetime risk of cancer after childhood exposure; therefore, a given radiation dose to a child is of greater public health significance than the same dose in an adult.¹
• Children are inherently more sensitive to radiation simply because they have more dividing cells and radiation basically acts on dividing cells and children have more time to express a cancer than do adults.⁴
• Much data ultimately derived from Japanese atomic bomb survivors. At exposure doses relevant to doses used in CT exams, there does not appear to be a threshold in dose below which no excess risk exists.⁷
  

Citation

1. Brenner D, et al. Estimated risks of radiation-induced fatal cancer from pediatric CT. Am J Roentgenol 2001; 176: 289-96
2. Karlsson P, et al. Intracranial tumors after exposure to ionizing radiation during infancy: a pooled analysis of two Swedish cohorts of 28,008 infants with skin hemangioma.
3. Sternberg S. CT scans in children linked to cancer later. USA Today. January 22, 2001,:1
4. Berdon WE. Editorial commentary on Roebuck DJ: Risk and benefit in paediatric radiology. Pediatr Radiol 1999;29:721.
5. Brenner DJ. Estimating cancer risks from pediatric CT: going from the qualitative to the quantitative. Pediatr Radiol. 2002; 32:228-231.
6. Preston DL, et al. Studies of mortality of atomic bomb survivors. Report 13: Solid cancer and noncancer disease mortality: 1950-1997. Radiat Res. 2003 160:381-407.

CAT Author: Brian J Drozdowski, MD

CAT Appraisers: John Frohna, MD

Date appraised: June 2, 2004