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

Abstract

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.

An Exponential Growth in Incidence of Thyroid Cancer: Trends and Impact of CT Imaging

“…The mean radiation dose to the thyroid from a CT scan of the neck ranges from 17-34 mGy, which is within the range that may increase the risk for thyroid cancer in children. [18][19][20] However, most people receiving neck CT scans are older adults, and the risk for cancer from radiation exposure decreases sharply with increasing age. 21 Pooled analyses of studies of thyroid cancer in patients exposed to radiation found that there was little risk for excess cancer when exposure was after age 20 years.…”

Performance of Iterative Image Reconstruction in CT of the Paranasal Sinuses: A Phantom Study

“…Due to a typically younger patient population and the proximity of radiosensitive organs such as the eye lenses and thyroid gland, increased concern is focused on radiation dosage. 4,5 Given the relatively small diameter of the head in comparison with the trunk and the high intrinsic contrast of the evaluated structures, CT can be performed with adapted dose parametersdepending on the indication. 2,6 Reducing the tube current is eventually limited by increased noise leading to a decrease in image quality, however.…”

The Epidemic of Thyroid Cancer in the United States: The Role of Endocrinologists and Ultrasounds

“…The thyroid gland exposure during a head and neck CT scan is up to 52.0 mGy (17). Neck CT scans are associated with an increased risk of developing thyroid cancer up to 390 per million patients (17). Chemical exposure should also be considered.…”