Thyroid doses in Ukraine due to 131I intake after the Chornobyl accident. Report I: revision of direct thyroid measurements

Abstract

The increased risk of thyroid cancer among individuals exposed during childhood and adolescence to Iodine-131 ( 131 I) is the main statistically significant long-term effect of the Chornobyl accident. Several radiation epidemiological studies have been carried out or are currently in progress in Ukraine, to assess the risk of radiation-related health effects in exposed populations. About 150,000 measurements of 131 I thyroid activity, so-called 'direct thyroid measurements', performed in May-June 1986 in the Ukrainian population served as the main sources of data used to estimate thyroid doses to the individuals of these studies. However, limitations in the direct thyroid measurements have been recently recognized including improper measurement geometry and unknown true values of calibration coefficients for unchecked thyroid detectors. In the present study, a comparative analysis of 131 I thyroid activity measured by calibrated and unchecked devices in residents of the same neighboring settlements was conducted to evaluate the correct measurement geometry and calibration coefficients for measuring devices. As a result, revised values of 131 I thyroid activity were obtained. On average, in Vinnytsia, Kyiv, Lviv and Chernihiv Oblasts and in the city of Kyiv, the revised values of the 131 I thyroid activities were found to be 10-25% higher than previously reported, while in Zhytomyr Oblast, the values of the revised activities were found to be lower by about 50%. New sources of shared and unshared errors associated with estimates of 131 I thyroid activity were identified. The revised estimates of thyroid activity are recommended to be used to develop an updated Thyroid Dosimetry system (TD20) for the entire population of Ukraine as well as to revise the thyroid doses for the individuals included in post-Chornobyl radiation epidemiological studies: the Ukrainian-American cohort of individuals exposed during childhood and adolescence, the Ukrainian in utero cohort and the Chornobyl Tissue Bank.

Assessment of Uncertainties and Errors in Post-Chernobyl Dosimetry

“…The coefficient of variation of the device's calibration coefficient that determined the measured 131 I thyroid activity for non-collimated SRP-68-01 device for different age groups was 0.06–0.10, while the coefficient of variation due to all geometry factors was 0.24–0.60 ( 44 ). For the SRP-68-01 device equipped with a lead collimator, the overall coefficient of variation associated with the device response during the measurements of 131 I varied from 0.29 to 0.50 ( 43 ).…”

“…Errors and uncertainties associated with the unknown calibration coefficients for unchecked devices used to measure thyroid radioactivity. A comparative analysis of 131 I thyroid activity measured by calibrated and unchecked devices in residents of the same or neighboring settlements was conducted to evaluate the correct measurement geometry and estimate the device-dependent adjustment factor for correcting the results of measurements done in Ukraine by unchecked devices used to measure the radioactivity in the thyroid ( 43 ). This introduced a new (compared to the random unshared errors considered in the previous section) shared (systematic) error associated with the estimates of the adjustment factor-values.…”

“…This introduced a new (compared to the random unshared errors considered in the previous section) shared (systematic) error associated with the estimates of the adjustment factor-values. The coefficient of variation of shared relative errors ranged among devices used to measure members of the Ukrainian-American cohort and Ukrainian cohort of persons exposed in utero from 0.12 for the SRP-69-01 device to 0.76 for a single-channel scintillation gamma-spectrometer, namely the GTRM-01ts ( 43 ).…”

“…Classification of errors associated with measured 131 I thyroid activity. The following sources of errors in measured 131 I thyroid activity can be considered as follows ( 43 ): (i) unshared classical errors associated with device response associated with impulse registration by device and individual anthropometric characteristics of measured person, i.e., thyroid volume, thyroid location, etc. ; (ii) unshared Berkson errors associated with the deviation of the thyroid detector's position from the proper geometry of measurements; and (iii) shared Berkson errors associated with the corrections of the calibration coefficients and estimation of proper measurement geometry for the uncalibrated gamma-spectrometers or the SRP-68-01 devices.…”

Current and emerging technologies for the remediation of difficult-to-measure radionuclides at nuclear sites

“…All of 129 I, 99 Tc, 90 Sr and 3 H emit beta particles, 21 which can result in health issues for humans if significant quantities build in the body through ingestion or inhalation. For example, thyroid cancers can be caused by both 129 I 51 and 99 Tc 52 exposure, and skeletal abnormalities can develop as a result of 90 Sr incorporation into bones. 53 Whilst 3 H does not accumulate in specific parts of the body, the 10 day and 40 day biological half-lives of tritiated water and OBT, respectively, make the radionuclide a potential hazard once inside humans.…”