Morteza Majidi Ata - School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
Abbas Moradi - Department of Social Medicine, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
Farideh Gharekhanloo - Department of Radiology, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran
Safoora Nikzad - Department of Medical Physics, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran

Background: Despite significant diagnosis benefits, the usage of ionizing radiation is not risk-free. The aim of this study was to determine the risk of thyroid cancer for children who exposed to brain computed tomography (CT) scan.Method: In this cross-sectional study, ۹۰ patients under ۲۰ years of age who underwent brain CT-scan were selected. Parameters such as age, sex, imaging technique, imaging characteristics, and thyroid absorbed dose were considered. We used SPSS software, version ۲۱, at ۹۵% confidence interval to analyze the absorbed dose and risk for each individual.Results: The mean and standard deviation of absorbed doses for girls and boys for the spiral technique were ۳.۹۵۴±۰.۳۹۳ and ۴.۷۲±۰.۰۰۰ mGy, and in sequential technique, were ۲.۲۸۲±۰.۴۶۱ and ۱.۹۸۵±۰.۴۳۱ mGy, respectively. The mean and standard deviation of the absorbed doses in <۵ years age group were ۵.۶۵±۲.۰۰, ۳.۰۳±۱.۳۴ in ۶ to ۱۰ years, ۲.۶۳±۰.۹۸ in ۱۱ to ۱۵ years, and in ۱۶ to ۲۰ years were ۲.۵۷±۱.۰۴ mGy (P < ۰.۰۰۱). There was a significant negative correlation between the absorbed dose and field dimensions (r = -۰.۶۰۴, P < ۰.۰۰۱) and slice thickness (r = -۰.۷۷۷, P < ۰.۰۰۱). The mean and standard deviation of Lifetime risk for thyroid cancer induction (×۱۰۵) in <۵ years age group in spiral technique was ۱۵۸.۷۹±۳۲۲.۵۰ for female subjects and ۱۶.۵±۴۲.۹۰ for male patients, which was significantly more than those of other groups and techniques (P < ۰.۰۰۱).Conclusion: The rate of thyroid absorbed dose during brain CT-scan was found to be noticeable, especially in spiral CT imaging, for female patients < ۵ years. Based on our results, it was associated with an increased risk of thyroid cancer in this age group.

Computed Tomography, Thyroid Dose, Cancer Risk, children