The catchy title comes from a Lancet editorial (Lancet 2012; 380: 455-57); the related article (Lancet 2012; 380: 499-505) details the radiation risk posed by CT scans.
While concerns about imaging radiation exposure have become commonplace, the evidence for the risk has been more in the theoretical realm rather than proven. That is, the risk projection models were based on studies of survivors of the atomic bombs in Japan.
The retrospective study in Lancet examines 178,604 children who underwent CT between 1985-2002. Typical followup was 10 years (maximum followup of 23 years). None of these children had cancer at the time of CT. The study determined the number of leukemias that developed more than 2 years following CT and brain tumors which occurred more than 5 years after CT. This lag time was done to avoid any confounding of cancer that may have been present and not detected at time of CT.
- 74 patients developed leukemia and 135 developed brain tumors. There was a dose-related risk: 0.036/mGy for leukemia and 0.023/mGy for brain tumors. Thus, the relative risk of leukemia in patients who had at least 30 mGy was 3.18; whereas, brain cancer risk for a cumulative dose of > 50 mGy was 2.82. [1 mGy=1 mSv]
- If typical doses of CT administered, 2-3 head CTs could triple the risk of a brain tumor and 5-10 head CTs could triple the risk of leukemia.
- The absolute risk remains low. In patients less than 10 years, one excess case of leukemia and one brain tumor would be expected for 10,000 head CT scans.
Goal with CT scans:
- ALARA: as low as reasonably achievable –for every study. Newer protocols allow lower radiation doses while preserving good image quality.
- Think carefully about each CT. It is estimated that 20-50% of CTs could be replaced with another type of imaging or not done at all.
For the skeptics about the risk of CT scans, the editorialist concludes that this study confirms “that CT scans almost certainly produce a small cancer risk…we must redouble our efforts to justify and optimize every CT scan.”
Related blog entries:
- -AJR 2001; 176: 289-96. Estimated risks of radiation-induced fatal cancer from pediatric CT
- -Br J Radiol 2012; 85: 523-28. Justification of CTs -some not needed
- -AJR 2010; 194: 868-73. Lower CT radiation doses in pediatric patients. ‘Image gently’
- -Arch Intern Med 2009; 169: 2078-86.