Thyroid dose from common head and neck CT examinations in children: is there an excess risk for thyroid cancer induction?

This study was conducted to estimate thyroid dose and the associated risk for thyroid cancer induction from common head and neck computed tomography (CT) examinations during childhood. The Monte Carlo N-particle transport code was employed to simulate the routine CT scanning of the brain, paranasal sinuses, inner ear and neck performed on sequential and/or spiral modes. The mean thyroid dose was calculated using mathematical phantoms representing a newborn infant and children of 1year, 5 years, 10 years and 15 years old. To verify Monte Carlo results, dose measurements were carried out on physical anthropomorphic phantoms using thermoluminescent dosemeters (TLDs). The scattered dose to thyroid from head CT examinations varied from 0.6 mGy to 8.7 mGy depending upon the scanned region, the pediatric patient's age and the acquisition mode used. Primary irradiation of the thyroid gland during CT of the neck resulted in an absorbed dose range of 15.2-52.0 mGy. The mean difference between Monte Carlo calculations and TLD measurements was 11.8%. Thyroid exposure to scattered radiation from head CT scanning is associated with a low but not negligible risk of cancer induction of 4-65 per million patients. Neck CT can result in an increased risk for development of thyroid malignancies up to 390 per million patients.