Objective: Computer tomography (CT) involves ionizing X-irradiation which can cause DNA damage from free radicals. CT use has risen dramatically due to its high speed and diagnostic value but it leads to an estimated lifetime cancer risk of up to 4% with highest risk for children. Double strand breaks, the most serious DNA damage caused by X-rays and other types of ionizing radiation, leads to histone H2AX phosphorylation which causes recruitment of repair proteins to DNA damage sites. γH2AX foci therefore represent quantitatively double strand breaks and can be assayed by a fluorescent immunostaining procedure. This γH2AX assay has been shown to be useful as a reliable biodosimeter for X-irradiation in vitro, in animals, and in adults. Recently also children who received cardiac catheterization procedures involving fluoroscopy with intermediate X-irradiation doses showed a dose response in this assay. We tested whether the γH2AX assay can detect changes when children receive X-irradiation at very low doses (<3 mSv) from CT scans. Methods: For this pilot study, three children aged 3 to 21 months and scheduled for a medically indicated CT were recruited through the emergency department at Kapi'olani Medical Center (Honolulu, Hawaii). These children donated blood immediately before and 1 hour after their CT exam (1.57- 2.86 mSv). Blood was immediately processed after the second blood draw and lymphocytes were isolated and fixed. For a blind analysis, the samples were coded in duplicate and shipped to Columbia University, New York, where the lymphocytes were immunolabeled with an anti-human γH2AX monoclonal antibody. The average number of γH2AX foci per cell nucleus was determined for each of the duplicate samples. Results: The γH2AX assay showed that the fluorescent frequencies were dose dependently higher in all patients 1 hour after CT exposure as compared to before CT (p=0.046 by paired t-test). Conclusion: In this pilot study we observed a significant induction of γH2AX foci in lymphocytes after very low dose ionizing X-irradiation (1-3 mSv) in vivo in children one hour after CT.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4347. doi:1538-7445.AM2012-4347