Prevalence of goiter and urinary iodine excretion levels in children around Chernobyl

Ultrasonography-based reference values for the cross-sectional area of the thyroid gland in children and adolescents: The Fukushima Health Management Survey

We previously described the thyroid volume, which was calculated by measuring the thyroid width, thickness, and longitudinal length using ultrasonography, in children and adolescents. We have proposed a simplified method for quantitatively assessing the thyroid size, to overcome the inaccuracy and challenges in measuring the longitudinal length of the thyroid. Based on measurements of 317,847 (girls: 156,913, boys: 160,934) children and adolescents, we calculated sex-specific means and standard deviations of thyroid width and thickness, and of the cross-sectional area computed by multiplying them, for every age and 0.1 m² of body surface area, after ensuring normal distribution with Box-Cox transformation. Multivariate regression analysis revealed that female sex, age, and body surface area were independently associated with areas of each thyroid lobe. Our novel method may be useful in quantitatively assessing the thyroid size, and appropriately diagnosing pathological conditions, such as hypoplasia, atrophy, and enlargement of the thyroid gland, in children and adolescents.

Radiation Exposure to the Thyroid After the Chernobyl Accident

INTRODUCTION

The Chernobyl accident resulted in a considerable release of radioactivity to the atmosphere, particularly of Iodine-131 (¹³¹I), with the greatest contamination occurring in Belarus, Ukraine, and western part of Russia.

MATERIAL AND METHODS

Increase in thyroid cancer and other thyroid diseases incidence in population exposed to Chernobyl fallout in these counties was the major health effect of the accident. Therefore, a lot of attention was paid to the thyroid doses, mainly, the ¹³¹I intake during two months after the accident. This paper reviews thyroid doses, both the individual for the subjects of radiation epidemiological studies and population-average doses. Exposure to ¹³¹I intake and other exposure pathways to population of affected regions and the Chernobyl cleanup workers (liquidators) are considered.

RESULTS

Individual thyroid doses due to ¹³¹I intake varied up to 42 Gy and depended on the age of the person, the region where a person was exposed, and their cow's milk consumption habits. Population-average thyroid doses among children of youngest age reached up to 0.75 Gy in the most contaminated area, the Gomel Oblast, in Belarus. Intake of ¹³¹I was the main pathway of exposure to the thyroid gland; its mean contribution to the thyroid dose in affected regions was more than 90%. The mean thyroid dose from inhalation of ¹³¹I for early Chernobyl cleanup workers was estimated to be 0.18 Gy. Individual thyroid doses due to different exposure pathways varied among 1,137 cleanup workers included in the epidemiological studies up to 9 Gy. Uncertainties associated with dose estimates, in terms of mean geometric standard deviation of individual stochastic doses, varied in range from 1.6 for doses based on individual-radiation measurements to 2.6 for "modelled" doses.

CONCLUSION

The ¹³¹I was the most radiologically important radionuclide that resulted in radiation exposure to the thyroid gland and cause an increase in the of rate of thyroid cancer and other thyroid diseases in population exposed after the Chernobyl accident.

Major Factors Affecting Incidence of Childhood Thyroid Cancer in Belarus after the Chernobyl Accident: Do Nitrates in Drinking Water Play a Role?

One of the major health consequences of the Chernobyl Nuclear Power Plant accident in 1986 was a dramatic increase in incidence of thyroid cancer among those who were aged less than 18 years at the time of the accident. This increase has been directly linked in several analytic epidemiological studies to iodine-131 (¹³¹I) thyroid doses received from the accident. However, there remains limited understanding of factors that modify the ¹³¹I-related risk. Focusing on post-Chernobyl pediatric thyroid cancer in Belarus, we reviewed evidence of the effects of radiation, thyroid screening, and iodine deficiency on regional differences in incidence rates of thyroid cancer. We also reviewed current evidence on content of nitrate in groundwater and thyroid cancer risk drawing attention to high levels of nitrates in open well water in several contaminated regions of Belarus, i.e. Gomel and Brest, related to the usage of nitrogen fertilizers. In this hypothesis generating study, based on ecological data and biological plausibility, we suggest that nitrate pollution may modify the radiation-related risk of thyroid cancer contributing to regional differences in rates of pediatric thyroid cancer in Belarus. Analytic epidemiological studies designed to evaluate joint effect of nitrate content in groundwater and radiation present a promising avenue of research and may provide useful insights into etiology of thyroid cancer.

Thyroid Dose Estimates for a Cohort of Belarusian Children Exposed to (131)I from the Chernobyl Accident: Assessment of Uncertainties

Deterministic thyroid radiation doses due to iodine-131 ((131)I) intake were reconstructed in a previous article for 11,732 participants of the Belarusian-American cohort study of thyroid cancer and other thyroid diseases in individuals exposed during childhood or adolescence to fallout from the Chernobyl accident. The current article describes an assessment of uncertainties in reconstructed thyroid doses that accounts for the shared and unshared errors. Using a Monte Carlo simulation procedure, 1,000 sets of cohort thyroid doses due to (131)I intake were calculated. The arithmetic mean of the stochastic thyroid doses for the entire cohort was 0.68 Gy. For two-thirds of the cohort the arithmetic mean of individual stochastic thyroid doses was less than 0.5 Gy. The geometric standard deviation of stochastic doses varied among cohort members from 1.33 to 5.12 with an arithmetic mean of 1.76 and a geometric mean of 1.73. The uncertainties in thyroid dose were driven by the unshared errors associated with the estimates of values of thyroid mass and of the (131)I activity in the thyroid of the subject; the contribution of shared errors to the overall uncertainty was small. These multiple sets of cohort thyroid doses will be used to evaluate the radiation risks of thyroid cancer and noncancer thyroid diseases, taking into account the structure of the errors in the dose estimates.

Thyroid ultrasound findings in children from three Japanese prefectures: Aomori, Yamanashi and Nagasaki

Due to the likelihood of physical and mental health impacts following the unprecedented accident at the Fukushima Dai-ichi Nuclear Power Plant, the Fukushima prefectural government decided to conduct the Fukushima Health Management Survey to assist in the long-term health management of residents. This included thyroid ultrasound examination for all children in Fukushima. For appropriate evaluation of ultrasound screening of the thyroid, it is important to understand its reference data of thyroid findings in children in general. In order to analyze the frequencies of specific thyroid findings, we conducted ultrasound screening of the thyroid by the same procedures as used in Fukushima in 4,365 children, aged 3 to 18 years, from three Japanese prefectures. Overall, thyroid cysts were identified in 56.88% and thyroid nodules in 1.65% of the participants. Thyroid cysts and nodules with a maximum diameter of more than 5 mm were identified in 4.58% and 1.01%, respectively, and age-adjusted prevalences were 3.82% and 0.99%, respectively. Although the prevalence of cysts and nodules varied among the examination areas, no significant differences were observed among the three examination areas in the prevalence of cysts and nodules with a maximum diameter of more than 5 mm. Also, the prevalence of thyroid cysts and nodules, especially those with a maximum diameter of more than 5 mm, significantly increased with age, and showed a female predominance. We also identified ectopic thymus (1.95%), diffuse goiter (1.40%), ultimobranchial body (0.73%), lymph node swelling (0.21%) and thyroid agenesis (0.05%). This is the first ultrasound description of the age-adjusted prevalence of thyroid cysts and nodules, or of the prevalence of abnormalities other than cysts and nodules, such as ectopic thymus, in relation to age, in the general Japanese child population. We contend that this can provide relevant information for the Fukushima Health Management Survey and future population studies.

Urinary iodine concentrations of pregnant women in Ukraine

BACKGROUND

Iodine requirements increase during pregnancy and previous studies have reported the inadequate iodine status of pregnant women in areas that have achieved iodine sufficiency in the general population. We examined the urinary iodine (UI) concentrations of pregnant women in Ukraine, where the iodine status is showing improvement among the general population.

METHODS

We enrolled 148 pregnant women<16 weeks pregnant and 80 healthy women as a control group living in Zhitomir, Ukraine. UI concentration, thyroid-stimulating hormone (TSH), antithyroglobulin antibodies (TGAb), and antithyroid peroxidase antibodies (TPOAb) were measured.

RESULTS

The median UI concentrations were significantly lower in pregnant women than in control women [13.0 (ND–51.0) μg/L vs. 62.0 (35.3–108.5) μg/L, p<0.001]. TSH concentrations were significantly lower in pregnant women than in control women [1.7 (1.2–2.7) IU/L vs. 2.2 (1.4–3.1) IU/L, p=0.011], but this difference disappeared when adjusted for age (2.1±0.1 IU/L vs. 2.4±0.2 IU/L, p=0.097). The frequency of TSH over 6.2 IU/L and the frequency of positive TGAb and/or TPOAb were not statistically different between groups (p=0.70 and p=0.48, respectively). The UI concentrations of 142 pregnant women (95.9%) were <150 μg/L indicating insufficient iodine intake.

CONCLUSIONS

The UI concentration of pregnant women in Ukraine revealed severe iodine deficiency. Regular monitoring and appropriate nutrition education are essential because iodine deficiency can be easily prevented by adequate iodine intake. The risk of iodine deprivation during pregnancy needs to be assessed locally over time because it may occur in areas that are not globally recognized as being iodine-deficient.

Thyroid dose estimates for a cohort of Belarusian children exposed to radiation from the Chernobyl accident

The U.S. National Cancer Institute, in collaboration with the Belarusian Ministry of Health, is conducting a study of thyroid cancer and other thyroid diseases in a cohort of about 12,000 persons who were exposed to fallout from the Chernobyl accident in April 1986. The study subjects were 18 years old or younger at the time of exposure and resided in Belarus in the most contaminated areas of the Gomel and Mogilev Oblasts, as well as in the city of Minsk. All cohort members had at least one direct thyroid measurement made in April-June 1986. Individual data on residential history, consumption of milk, milk products and leafy vegetables as well as administration of stable iodine were collected for all cohort members by means of personal interviews conducted between 1996 and 2007. Based on the estimated (131)I activities in the thyroids, which were derived from the direct thyroid measurements, and on the responses to the questionnaires, individual thyroid doses from intakes of (131)I were reconstructed for all cohort members. In addition, radiation doses to the thyroid were estimated for the following minor exposure pathways: (a) intake of short-lived (132)I, (133)I and (132)Te by inhalation and ingestion; (b) external irradiation from radionuclides deposited on the ground; and (c) ingestion intake of (134)Cs and (137)Cs. Intake of (131)I was the major pathway for thyroid exposure; its mean contribution to the thyroid dose was 92%. The thyroid doses from (131)I intakes varied from 0.5 mGy to almost 33 Gy; the mean was estimated to be 0.58 Gy, while the median was 0.23 Gy. The reconstructed doses are being used to evaluate the risk of thyroid cancer and other thyroid diseases in the cohort.

Thyroid consequences of the fukushima nuclear reactor accident

BACKGROUND

A special report, 'The Fukushima Accident', was delivered at the 35th Annual Meeting of the European Thyroid Association in Krakow on September 11, 2011, and this study is the follow-up of the special report.

OBJECTIVES

To present a preliminary review of potential thyroid consequences of the 2011 Fukushima nuclear reactor accident.

METHODS

Numerous new data have been presented in Japanese, and most of them are available on the website from each research institute and/or from each municipality. The review was made using these data from the website.

RESULTS

When individual radiation doses were expressed as values in more than 99% of residents, radiation doses by behavior survey in evacuation and deliberate evacuation areas were less than 10 mSv in the first 4 months, and internal radiation doses measured by whole body counters were less than 1 mSv/year. Individual thyroid radiation doses were less than 50 mSv (intervention levels) even in evacuation areas. As for health consequences, no one died and no one suffered from acute effects. The thyroid ultrasound examination is in progress and following examination of almost 40,000 children, 35% of them have nodules and/or cysts but no cancers.

CONCLUSIONS

Countermeasures against radiation must consider current individual measured values, although every effort must be taken to reconstruct radiation doses as precisely as possible. At present, the difference of thyroid radiation dose between Chernobyl and Fukushima appears to be due to the strict control of milk started within a week after the accident in Fukushima. Since the iodine-131 plume moved around in wide areas and for a long time, the method of thyroid protection must be reconsidered.

Urinary Iodine and Goiter Prevalence in Belarus: experience of the Belarus-American cohort study of thyroid cancer and other thyroid diseases following the Chornobyl nuclear accident

BACKGROUND

Because iodine deficiency can influence background rates of thyroid disease or modify radiation dose-response relationships, we compiled descriptive data on iodine status among participants in a Belarusian-American screening study who were exposed in childhood to radioiodine fallout from the Chornobyl nuclear accident. We have used the data from two consecutive screening cycles to examine whether indicators of iodine status changed before and after documented government initiatives to improve iodine intake.

METHODS

Urinary iodine concentrations in spot samples and prevalence of diffuse goiter by palpation were assessed in 11,676 exposed subjects who were 18 years or younger at the time of the accident on April 26, 1986, and were screened beginning 11 years later in connection with the Belarus-American Thyroid Study. Data for the first ( January 1997-March 2001) and second (April 2001-December 2004) screening cycles, which largely correspond to time periods before and after official iodination efforts in 2000/2001, were compared for the cohort overall as well as by oblast of residence (i.e., state) and type of residency (urban/rural).

RESULTS

Median urine iodine levels among cohort members increased significantly in the later period (111.5 mg/L) compared to the earlier (65.3 mg/L), with the cycle 2 level in the range defined as adequate iodine intake by the World Health Organization. During the same period, a significant decline in diffuse goiter prevalence was also observed. In both cycles, urinary iodine levels were lower in rural than in urban residents. Urinary iodine levels, but not rates of goiter, varied by oblast of residence. In both periods, adjusted median urine iodine concentrations were similar in Gomel and Minsk oblasts, where *89% of cohort members resided, and were lowest in Mogilev oblast. Yet Mogilev oblast and rural areas showed the most marked increases over time.

CONCLUSIONS

Trends in urinary iodine concentrations and prevalence of diffuse goiter by palpation suggest that iodination efforts in Belarus were successful, with benefits extending to the most iodine-deficient populations. Iodine status should be considered when evaluating thyroid disease risk in radioiodine-exposed populations since it can change over time and may influence rates of disease and, possibly, dose-response relationships

Calculation of electron dose to target cells in a complex environment by Monte Carlo code "CELLDOSE"

BACKGROUND

We used the Monte Carlo code "CELLDOSE" to assess the dose received by specific target cells from electron emissions in a complex environment. (131)I in a simulated thyroid was used as a model.

METHODS

Thyroid follicles were represented by 170 microm diameter spherical units made of a lumen of 150 microm diameter containing colloidal matter and a peripheral layer of 10 microm thick thyroid cells. Neighbouring follicles are 4 microm apart. (131)I was assumed to be homogeneously distributed in the lumen and absent in cells. We firstly assessed electron dose distribution in a single follicle. Then, we expanded the simulation by progressively adding neighbouring layers of follicles, so to reassess the electron dose to this single follicle implemented with the contribution of the added layers.

RESULTS

Electron dose gradient around a point source showed that the (131)I electron dose is close to zero after 2,100 microm. Therefore, we studied all contributions to the central follicle deriving from follicles within 12 orders of neighbourhood (15,624 follicles surrounding the central follicle). The dose to colloid of the single follicle was twice as high as the dose to thyroid cells. Even when all neighbours were taken into account, the dose in the central follicle remained heterogeneous. For a 1-Gy average dose to tissue, the dose to colloidal matter was 1.168 Gy, the dose to thyroid cells was 0.982 Gy, and the dose to the inter-follicular tissue was 0.895 Gy. Analysis of the different contributions to thyroid cell dose showed that 17.3% of the dose derived from the colloidal matter of their own follicle, while the remaining 82.7% was delivered by the surrounding follicles. On the basis of these data, it is shown that when different follicles contain different concentrations of (131)I, the impact in terms of cell dose heterogeneity can be important.

CONCLUSION

By means of (131)I in the thyroid as a theoretical model, we showed how a Monte Carlo code can be used to map electron dose deposit and build up the dose to target cells in a complex multi-source environment. This approach can be of considerable interest for comparing different radiopharmaceuticals as therapy agents in oncology.