| Hamilton et al., Seattle, WA, USA, studied a selected cohort of 5.199 persons who were exposed between 1944-57 to I-131 as during that period documents revealed that approximately 740,000 Curies of I-131 were released from the Hanford Nuclear Site in Washington State. The estimated thyroid doses ranged from 0.008 mGy to 2842 mGy. The cumulative incidence for thyroid cancer was 0.55% and for benign nodules 7.2%. Dose-response analyses revealed no increase in either thyroid cancer or benign nodules with increasing thyroid radiation dose. The authors conclude that in contrast to the Chernobyl accident and the accident in the Marshall Islands, no evidence emerged that thyroid neoplasia increased in relation to I-131 irradiation from Hanford. This discrepancy may be explained by factors such as differences in type of radiation exposure, dose rate, chronic versus acute exposures, dose amplitude, and possibly dietary iodine intake. Shilin et al., Moscow, Russia, assessed the prevalence of circulating thyroid antibodies in a total group of 584 randomly selected children living in three mildly iodine deficient regions. The study was done between 1992-1996. Two regions were polluted by low levels of radiation (RR;137 Cs 1-10 Ci/km2) caused by the Chernobyl accident in April 1986 and the children were thus exposed 6 to 10 years before. The third region was not polluted and used as control. The data from the two exposed regions were combined. An equal prevalence of circulating Tg antibodies was found in both groups (exposed 7/423, 1.6% vs. control 2/152, 1%, NS). Microsomal antibodies (MAB) were more frequent in the exposed group (19.4% vs. 1.3%, p < 0.00001). Frequency and concentrations of MAB were higher when subjects were still in utero or during nursing than when older at the time of exposure (72/313, 23% and 1 : 3238 +/- 1 : 230 vs. 12/119, 10%, and 1 : 1296 +/- 1 : 423, p < 0.01 and p < 0.001, respectively). The presence of MAB was not associated with abnormal thyroid function or goiter but MAB carriers had hypoechogenic foci on ultrasound suggesting thyroiditis, 1.4 times more frequently than when MAB were not present. (Comment: It will be important from the patients' side but also from the scientific aspect if this increase in MAB is temporarily or permanent and will lead to thyroid dysfunction in the future and also if it is related to future carcinoma development or just the reverse, that it is of protective value, because of destruction of the thyroid gland.) |
