Thyroid Tumors Following 131 I or Localized X Irradiation to the Thyroid and Pituitary Glands in Rats

Ultrasound-Detected Thyroid Nodule Prevalence and Radiation Dose from Fallout

“…For example, Kocher et al (51) reasoned that, "Since the dose from irradiation by photons is due almost entirely to ionization produced by energetic secondary electrons, an REF (radiation effectiveness factor) for photons of a given energy represents the biological effectiveness of secondary electrons produced by first interactions of those photons in tissue," and that it is therefore reasonable to assign an REF of one to electrons of energy greater than 15 keV. Arguably the most relevant experimental study is that of Lee et al (52) in which adolescent Long-Evans rats exposed to localized external X rays or to injected 131 I, giving protracted doses to the thyroid between 0.8 and 10 Gy, were killed humanely and evaluated for thyroid tumors after 2 years, with similar dose responses for cancers associated with the two types of radiation, i.e., an RBE of one. A report of the U.S. National Council on Radiation Protection (53) questioned the relevance of the findings of Lee et al (52) to human thyroid cancer risk and recommended an RBE of 0.3 relative to medical X rays for radiation protection purposes as the highest credible value based on limited human data.…”

“…Arguably the most relevant experimental study is that of Lee et al (52) in which adolescent Long-Evans rats exposed to localized external X rays or to injected 131 I, giving protracted doses to the thyroid between 0.8 and 10 Gy, were killed humanely and evaluated for thyroid tumors after 2 years, with similar dose responses for cancers associated with the two types of radiation, i.e., an RBE of one. A report of the U.S. National Council on Radiation Protection (53) questioned the relevance of the findings of Lee et al (52) to human thyroid cancer risk and recommended an RBE of 0.3 relative to medical X rays for radiation protection purposes as the highest credible value based on limited human data. However, they also suggested that the value might be higher at low doses and at low dose rates.…”

The recognition of childhood thyroid cancer as a consequence of the Chernobyl accident: an allegorical tale of our time?

“…6 This was significantly larger than those that showed a lesser effect and it was subsequently concluded that it was the only study with sufficient statistical power. The findings of this study were confirmed by an independent review carried out under the auspices of the United States Department of Energy, but the report of the review was not published.…”

Radiation-Associated Thyroid Cancer - Facts and Fiction

“…One large experimental study contradicts these results, at least for thyroid doses below 4 Sv (17). There are several possible reasons for the lower carcinogenic effect: the thyroid gland could receive either very high cell-killing doses, or low doses from 131 I due to the non-uniformity of 131 I dose distribution within the thyroid gland (especially in hyperthyroid patients); the uncertainties in dose estimation are a greater problem for internal than for external exposures as shown by Becker (18), and the half-life of approximately 7 days for 131 I might allow DNA repair.…”