Radiation dose-response relationship provides best assessment for pediatric thyroid cancer risk

The linear dose-response relationship remains the most plausible method of determining risk for radiation-associated thyroid cancer among children, according to findings published in the Journal of Clinical Endocrinology and Metabolism.

“The increasing use of diagnostic and therapeutic medical procedures that involve radiation raises concerns about the consequences of low-dose irradiation on cancer occurrence and in particular whether linear-based extrapolations represent the best estimate of low dose cancer risk or whether a threshold dose, below which there is no risk of radiation-induced cancer, might exist,” Jay H. Lubin, PhD, of the division of cancer epidemiology and genetics at the National Cancer Institute, and colleagues wrote. “Questions about thyroid cancer risks at low thyroid radiation doses in children are best addressed using data in children exposed at low doses.”

Lubin and colleagues conducted a pooled analysis of data from nine cohort studies of childhood radiation exposure and thyroid cancer. Studies included two on childhood cancer survivors, six on children being treated for benign diseases and one on children who survived the atomic bombings in Japan. The researchers identified 252 cases of thyroid cancer across 2,588,559 person-years in patients who had been irradiated, and 142 cases across 1,865,957 person-years in patients who had not.

Risk ratios increased with thyroid radiation dose for doses < 0.2 Gy and < 0.1 Gy, Lubin and colleagues reported (P < .01), with neither departing significantly from linearity. The trend persisted more than 45 years after exposure, though it was greater at younger age of exposure and younger attained age. The relationship was similar across number of treatments and sexes, the researchers wrote. Estimated threshold doses ranged from zero to 0.03 Gy, with an upper 95% confidence bound of 0.04 Gy, they wrote.

“In conclusion, these analyses reinforced the existence of an excess thyroid cancer risk at doses < 0.2 Gy and < 0.1 Gy, and perhaps at even lower doses,” the researchers wrote. “The consistency of the linear radiation dose-response at low doses and the apparent absence of a significant radiation fractionation effect reaffirm that the direct application of a linear relationship remains the most plausible approach for the extrapolation of radiation-associated thyroid cancer risk and adds support to the use of a linear model for [as low as reasonably achievable] assessments.”

Disclosure: The researchers report no relevant financial disclosures.