THYROID SCREENING AND RELIABILITY OF RADIATION THYROID DOSES FOR THE BELARUSIAN IN UTERO COHORT.

OBJECTIVE: To describe the status and results of thyroid disease screening and assessment of reliability of radiationthyroid doses in the Belarusian in utero cohort of 2,965 individuals exposed to Chernobyl (Chornobyl) fallout. MATERIALS AND METHODS: Thyroid screening examinations are currently underway including thyroid palpation by anendocrinologist, ultrasonographic examination by an ultrasonographer and analysis of blood samples for diagnosisof hypo- and hyperthyroidism, autoimmune thyroiditis, thyroid function tests (thyroid-stimulating hormone [TSH],thyroxine [T4], thyroid peroxidase antibody [anti-TPO], and thyroglobulin antibodies [anti-TG]). Reliability of (i)information from 780 pairs of questionnaires obtained during the first and second interviews of the mothers and (ii)thyroid doses, which were calculated for the cohort members using this information, is evaluated. RESULTS: As of 15 August 2021, 1,267 in utero exposed study subjects had been screened. A single thyroid nodule wasdiagnosed in 167 persons (13.2 % of the total) and multiple thyroid nodules in 101 persons (8.0 %): 189 (14.9 %)persons had nodules detected for the first time at the screening while 79 (6.2 %) persons had nodules detected pre-viously (pre-screening nodules). Fifty-nine out of 268 subjects (22.0 %) with a suspicious thyroid nodule werereferred to fine needle aspiration biopsy, and among them 33 (55.9 %) were biopsied. Reasonable agreement wasobserved for modelqbased doses calculated for the Belarusian in utero cohort members using data from the two inter-views (Spearman's rank-correlation coefficient rs = 0.74, p < 0.001), while measurementqbased doses yielded almost per-fect agreement (rs = 0.99, p < 0.001). CONCLUSIONS: During the thyroid screening, at least one thyroid nodule was identified in 268 of 1,267 (21.2 %) inutero exposed cohort members. Seven thyroid cancer cases were identified in the cohort, including 5 pre-screeningcases and 2 cases detected during the screening. Ongoing research on this unique cohort will provide importantinformation on adverse health effects following prenatal and postnatal exposure to radioiodine and radiocesium iso-topes, for which available epidemiological data are scant.

Thyroid cancer risk in Belarus among children and adolescents exposed to radioiodine after the Chornobyl accident.

BACKGROUND: Previous studies showed an increased risk of thyroid cancer among children and adolescents exposed to radioactive iodines released after the Chornobyl (Chernobyl) accident, but the effects of screening, iodine deficiency, age at exposure and other factors on the dose-response are poorly understood. METHODS: We screened 11 970 individuals in Belarus aged 18 years or younger at the time of the accident who had estimated (131)I thyroid doses based on individual thyroid activity measurements and dosimetric data from questionnaires. The excess odds ratio per gray (EOR/Gy) was modelled using linear and linear-exponential functions. RESULTS: For thyroid doses <5 Gy, the dose-response was linear (n=85; EOR/Gy=2.15, 95% confidence interval: 0.81-5.47), but at higher doses the excess risk fell. The EOR/Gy was significantly increased among those with prior or screening-detected diffuse goiter, and larger for men than women, and for persons exposed before age 5 than those exposed between 5 and 18 years, although not statistically significant. A somewhat higher EOR/Gy was estimated for validated pre-screening cases. CONCLUSION: 10-15 years after the Chornobyl accident, thyroid cancer risk was significantly increased among individuals exposed to fallout as children or adolescents, but the risk appeared to be lower than in other Chornobyl studies and studies of childhood external irradiation.

Thyroid dose reconstruction for the population of Belarus after the Chernobyl accident.

An 131I environment transfer model--adapted for Belorussian conditions--was applied to estimate thyroid doses for different population groups. For this purpose the available data were analysed and the important radioecological parameters assessed i.e. (a) the elimination rate of 131I from grass due to weathering and growth dilution, (b) the initial interception of 131I by vegetation, (c) the transfer coefficient for 131I from grass to cow's milk, (d) the yield to pasture grass and (e) the milk consumption rate. Additionally, the influence of applied countermeasures has been taken into account, such as the interruption of locally produced milk consumption, and the appropriate correction factors have been estimated. As a result, the average age-dependent thyroid doses were assessed for the Belorussian population. The highest average doses in children (> 1 Gy) have been estimated for the Bragin, Khoiniki, Narovlia and Vetka raions of the Gomel oblast. The thyroid exposure tends to decrease from the southeastern (closest to the Chernobyl nuclear power plant areas) to the northwestern part of the republic. When comparing the assessed thyroid doses with estimates derived from direct 131I activity measurements in thyroids (for the locations with more than 15 direct measurements), the results agree fairly well. The model calculation may perhaps overestimate thyroid doses of the population residing in the settlements of the central and northern parts of Belarus, distant from the areas with direct measurements of 131I activities in soil, grass and milk. These thyroid dose estimates may serve as a basis for further epidemiological studies and risk analyses.

Influence of measurement geometry on the estimate of 131(I) activity in the thyroid: Monte Carlo simulation of a detector and a phantom.

An approach for evaluating the influence of measurement geometry on estimates of 131(I) in the thyroid from measurements with survey meters was developed using Monte Carlo simulation of radiation transport in the human body and the radiation detector. The modified Monte Carlo code, EGS4, including a newly developed mathematical model of detector, thyroid gland, and neck, was used for the computations. The approach was tested by comparing calculated and measured differential and integral detector characteristics. This procedure was applied to estimate uncertainties in direct thyroid-measurement results due to geometrical errors.

Emerging technological bases for retrospective dosimetry.

In this article we discuss examples of challenging problems in retrospective dosimetry and describe some promising solutions. The ability to make measurements by accelerator mass spectrometry and luminescence techniques promises to provide improved dosimetry for regions of Belarus, Ukraine and Russian Federation contaminated by radionuclides from the Chernobyl accident. In addition, it may soon be possible to resolve the large neutron discrepancy in the dosimetry system for Hiroshima through novel measurement techniques that can be used to reconstruct the fast-neutron fluence emitted by the bomb some 51 years ago. Important advances in molecular cytogenetics and electron paramagnetic resonance measurements have produced biodosimeters that show potential in retrospective dosimetry. The most promising of these are the frequency of reciprocal translocations measured in chromosomes of blood lymphocytes using fluorescence in situ hybridization and the electron paramagnetic resonance signal in tooth enamel.

The feasibility of using 129I to reconstruct 131I deposition from the Chernobyl reactor accident.

Radioiodine released to the atmosphere from the accident at the Chernobyl nuclear power station in the spring of 1986 resulted in large-scale thyroid-gland exposure of populations in Ukraine, Belarus, and Russia. Because of the short half life of 131I (8.04 d), adequate data on the intensities and patterns of iodine deposition were not collected, especially in the regions where the incidence of childhood-thyroid cancer is now increasing. Results are presented from a feasibility study that show that accelerator-mass-spectrometry measurements of 129I (half life 16 x 106 y) in soil can be used to reconstruct 131I-deposition density and thus help in the thyroid-dosimetry effort that is now urgently needed to support epidemiologic studies of childhood-thyroid cancer in the affected regions.

Radiation effects on the population of Belarus after the Chernobyl accident and the prediction of stochastic effects.

Evaluation of conditions of exposure during the post-accident period makes it possible to identify two periods in the radiation exposure of Belarus's population. As a result of our investigations we obtained data about doses for four different categories in the exposed population: people who lived in the contaminated territories without evacuation and relocation; evacuated people: cleanup workers ("liquidators"); and people who were exposed in childhood, especially for thyroid exposure. The total doses for these categories in different time periods were analysed. Evaluation of doses received by the Belarusian population due to the Chernobyl accident shows no evidence of doses, that could lead to the deterministic consequences of radiation exposure. For all exposed groups we made predictions about different types of stochastic consequences of exposure.

[Soft- and hardware support for the setup for computer tracking of radiation teletherapy]. / Programmnoe i apparaturnoe obespechenie kompleksa soprovozhdeniia distantsionnoi luchevoi terapii s pomoshch'iu EVM.

A hard and soft ware computer assisted complex has been worked out for gamma-beam therapy. The complex included all radiotherapeutic units, including a Siemens program controlled betatron with an energy of 42 MEV computer ES-1022, a Medigraf system of the processing of graphic information, a Mars-256 system for control over the homogeneity of distribution of dose rate on the field of irradiation and a package of mathematical programs to select a plan of irradiation of various tumor sites. The prospects of the utilization of such complexes in the dosimetric support of radiation therapy are discussed.

[Evaluation of radiation treatment effectiveness using the rated standard dose (RSD) under different irradiation conditions]. / Otsenka éffektivnosti luchevogo lecheniia s pomoshch'iu NSD pri razlichnykh usloviiakh oblucheniia.

In the evaluation of efficacy or while comparing various irradiation schemes with the help of the RSD concept one should consider the effect of various conditions of patient's irradiation (energy, a field size, dose rate, etc.) on the biological efficacy of absorbed energy. The radiobiological effect of various irradiation schemes should be evaluated by a common scale, therefore factors altering dose biological efficacy should be considered within the limits of the same RSD formula. In our opinion, there is no sense in individualizing the evaluation of an effect of the dose rate on the biological efficacy of radiotherapy as a separate RSD formula. The incorporation in the RSD formula of an empirical expression of RBE dependence on the dose rate within the range of 0.13-300 Gy/hr. and factors of the dependence of dose biological efficacy on its spatial distribution (energy, a field size) gives an opportunity not only to consider more correctly changes in patient's irradiation from session to session but also makes it possible to apply it to fractionated and protracted irradiation schemes.

[Computerized program for calculating the dose distribution generated by intracavitary linear sources of gamma radiation]. / Programma rascheta na EVM doznogo raspredeleniia, sozdavaemogo vnutripolostnymi lineimymi istochnikami gamma-izlucheniia.

One can achieve a high precision in the dosing of a session of intracavitary radiotherapy by rapid computerization of the treatment time that is necessary for obtaining a certain dose in a pathological focus taking account of an actual location of radiation sources in the process of irradiation. The authors have developed an algorithm and drawn up a program for computer ES-1022 to calculate a dose rate in any point of an irradiated volume from the system of gamma-radiation sources oriented arbitrarily in space. As part of a hard- and soft ware dosimetric complex, the above program provides for the calculation of the treatment time by a set dose; the time is necessary for supplying this dose to a tumor focus taking account of an actual location of radiation sources during a session of irradiation. The whole computer procedure from the moment of obtaining necessary anatomo-topographic information in the form of two x-ray pictures up to the output of an irradiation session time value and other information into the alpha-numeric printer takes 3-5 min. The program makes it possible to calculate dose distribution in any preset plane (up to 4 planes at a time) of an irradiated volume.