Iodine nutrition and the risk from radioactive iodine: a workshop report in the chernobyl long-term follow-up study.

The major fallout of radionuclides from the nuclear power station accident at Chernobyl on 26 April, 1986, occurred in regions of Ukraine and Belarus that are believed to be moderately deficient in dietary iodine. On 17 November, 2000, in conjunction with the Ukraine-Belarus-USA study of developing thyroid disease in a cohort of individuals exposed as children, a workshop was held to review what is known about iodine nutrition in the region, how this might influence the risk of thyroid tumor formation from radioiodine, and whether and how iodine nutrition should be monitored in this long-term project. This report is a summary of the workshop proceedings. Although no precise information about iodine intake in 1986 was found, the prevalence of mild goiter in the region's children suggested iodine deficiency and urinary iodine measurements begun in 1990 indicated that mild to moderate deficiency existed. Increased thyroid iodine uptake and increased thyroid size in 1986 resulting from iodine deficiency would have had counteracting influence on the thyroid radiation dose and knowledge of these parameters is required for dose reconstruction. More problematic is the possible role of iodine deficiency in the years following the accident. Theoretically, the resulting increase in thyroid cellular activity might increase the risk of tumorigenesis but experimental or clinical evidence supporting this hypothesis is meager or absent. Despite this limitation it was considered important to monitor iodine nutrition in the cohort subjects in relation to their place of residence and over time. Methods to accomplish this were discussed.

Pretreatment with propylthiouracil but not methimazole reduces the therapeutic efficacy of iodine-131 in hyperthyroidism.

Ninety-three hyperthyroid patients were treated with 1 dose of iodine-131 (131I) during the past 10 years. Thirty-three were pretreated with propylthiouracil (PTU), 22 with methimazole (MMI), and 38 received no antithyroid drugs (ATD). ATD were discontinued 5-55 days before 131I therapy in three fourths of the cases and more than 4 months before therapy in one fourth of the cases. The frequency of cures in the 3 groups, 6-8 months after radioiodine therapy, was retrospectively studied. The cure rate among those who discontinued PTU for 5-55 days before 131I was significantly reduced (24%), compared with those who discontinued MMI for the same duration (61%) or those who received no ATD (66%). When PTU was discontinued for more than 4 months, the cure rate was similar to those who received no ATD. It is concluded that if ATD are used as initial therapy for hyperthyroidism, then PTU (but not MMI) may reduce the therapeutic efficacy of subsequent 131I. The reduction in cure rate was observed even when PTU was discontinued for as long as 55 days before 131I therapy. To our knowledge, this is the first report to compare, in one study, the effects of pretreatment with PTU and MMI on 131I therapy.

129I, 131I and 127I in animal thyroids after the Chernobyl nuclear accident.

A small number of animal thyroids from Bad Hall, Austria; Ulm, Germany; and Steinkjer, Norway had 131I (half-life 8.06 d) measured between 21 and 72 d following the nuclear accident at Chernobyl on 26 April 1986. Nine years later 129I (half-life 1.57 x 10(7) y) fission product and natural 127I were measured in the same thyroids. The mass ratios, 129I/131I were calculated to the date of the Chernobyl accident and they ranged between 13 and 71. These ratios are compared to the expected ratios within an operating nuclear reactor during 2 y of operation, where the 129I/131I(-1) ratio never exceeded 30. The observed ratio of 129I to natural 127I in thyroids ranged from 5 to 200 times the ratio before the accident, except that the Norwegian thyroids had 129I/127I ratios which were less than the ratios of pre-Chernobyl thyroids from Ulm. These studies show the 129I and 131I from the Chernobyl accident were accumulated with natural 127I in animal thyroids but the isotope ratios, calculated to the release date, had wide ranges. The 131I radioactive exposure might be estimated from a fission product mixture by measuring 129I in thyroids long after the exposure to 131I, but the results would probably show a wide range of possibilities. The determining variables should be evaluated. We know of no previous data regarding both 131I and 129I in thyroid glands during the first 3 mo after the Chernobyl accident.

Papillary thyroid carcinoma: demographics, treatment, and outcome in eleven pediatric patients treated at a single institution.

We describe 11 cases (8 females, 3 males) of papillary thyroid carcinoma in children treated at St. Jude Children's Research Hospital over a 33-year period, and review the literature. Ages ranged from 7-25 years (median, 16 years). Six patients had primary papillary thyroid carcinoma. Five patients had secondary papillary thyroid carcinoma after treatment of Hodgkin's disease (n = 2), acute lymphoblastic leukemia (n = 2), and neuroblastoma (n = 1) with chemotherapy and cervical radiation. The typical presentation was either cervical lymphadenopathy or a thyroid mass of short duration. Treatment consisted of thyroidectomy, cervical lymph node dissection, and postoperative thyroid hormone replacement (n = 1), parathyroid reimplantation (n = 1), 131I ablation (n = 4), external-beam irradiation (n = 1), and chemotherapy with doxorubicin (n = 1) or carboplatin and topotecan (n = 1). Nine patients are alive without evidence of disease 3.0-22.4 years from diagnosis. One patient has persistent but stable disease 17.3 years after diagnosis. One patient relapsed with metastatic lung disease 0.3 years after the initial diagnosis. He continues to do well after a brief but unsustained complete radiographic remission of disease to combination chemotherapy with carboplatin and topotecan. Our review supports excellent long-term outcome for primary or secondary papillary thyroid carcinoma in pediatric patients although complications may require close follow-up in a multidisciplinary setting.

Urinary iodine excretion in Belarus children.

Casual urine samples were collected to determine iodine excretion of 1680 Belarus children during 1990-1994. The subjects, 8-16 years old, were from nine different regions of Belarus; 60% were from the Gomel oblast, which has been associated with relatively high levels of radioiodine fallout and increased incidence of thyroid cancer. Most of the median values indicate borderline/low iodine intake or mild iodine deficiency. Ranges were wide but 163 children excreted < 20 micrograms I/l urine and they should be considered severely deficient in iodine.