Korean-specific biokinetic model for iodine in radiological protection

Abstract

The International Commission on Radiological Protection (ICRP) recently adopted a detailed biokinetic model for systemic iodine with reference transfer coefficients based on typical worldwide dietary intakes of stable iodine. The regional data provided demonstrate that the ICRP reference thyroidal biokinetics may differ substantially across regions with atypically low or high dietary intakes of stable iodine. Importantly, the design of the ICRP model facilitates modifications of reference thyroidal kinetics based on regional dietary iodine intake. The present study extended the ICRP model to the South Korean population, whose dietary iodine intake is much higher than the global mean. The following three transfer coefficients were selected as targets for Korean-specific values: thyroidal uptake rate (λ 1), hormonal secretion rate (λ 4) and leakage rate of thyroidal organic iodine as inorganic iodide (λ 5). The Korean-specific values for λ 1, λ 4 and λ 5 were determined to be 4.48, 0.0086 and 0.0171 d−1, respectively, to yield the measurements of thyroidal iodine and physiological status of Korean adults. The determined λ 1 and λ 5 values differed noticeably from the ICRP values, whereas the λ 4 value was comparable to that of the ICRP. Compared with the ICRP reference model, the Korean model, in which the Korean-specific transfer coefficients were adopted, predicted noticeably lower thyroidal uptake and faster decrease of thyroidal iodine. In addition, the predicted cumulative activities of radioiodine in the thyroid were substantially lower (40–80%) than those predicted by the ICRP model. The Korean model developed in this study demonstrates that the iodine biokinetics for Koreans (i.e. a population with a high iodine consumption) obviously differ from the prediction of the ICRP model. Hence, the Korean model may serve to improve the accuracy of thyroid dose estimation for Koreans and will lead to practical changes in matters concerned with radiological protection.

Age-Specific Thyroid Internal Dose Estimation for Koreans

“…In addition, the decrease in thyroidal iodine after 1 day was also faster in the Korean model. These deviations from the predictions of the Leggett's model [2] can be explained in the same way as in the Korean adult model development [6]. In brief, these differences result from the faster thyroid uptake rate of blood inorganic iodide and the shorter biological half-life in the thyroid.…”

“…First, the age-specific turnover times of extra-thyroidal organic iodine discussed by Leggett [2] (i.e., 4, 4.5, 5, 5.5, and 6 days in infants, at ages 1, 5, 10, and 15 years, respectively) and the ratios of these times to the corresponding time for adults (i.e., 7 days) were directly applied to Koreans. Because a turnover time of extra-thyroidal organic iodine in the ICRP adult model was not changed in the Korean adult model due to a lack of data for Koreans (see Section 2.3 in [6]), the transfer coefficients involved in the biokinetics of extra-thyroidal organic iodine were directly taken from the baseline values of Leggett's model [2]. However, for the biological half-life of thyroidal organic iodine showing a significant difference between the Korean adult model and the ICRP model, the baseline values proposed by Leggett [2] cannot be directly used.…”

“…The differences described above were observed in an identical fashion, regardless of age. A more in-depth discussion can be found in a previous study on Korean adult model development [6].…”

“…For South Koreans, one of the high-iodine-consuming populations, the mean daily iodine intake has been reported to range from 780 µg • d -1 [4] to a few thou-JRPR sand μg • d -1 [5]. For this reason, iodine biokinetic models have been developed specifically for South Koreans, reflecting the Korean-specific thyroid biokinetics, and a model for adult Koreans was proposed in a previous study [6]. In the development of the Korean model, it was concluded that transfer coefficients for thyroidal uptake rate, hormonal secretion rate, and leakage rate of thyroidal organic iodine as inorganic iodide were significantly different from those in ICRP reference model, and the Korean-specific values were determined to yield measurements of thyroidal iodine and physiological status of Korean adults (see Section 2.4 in [6]).…”

Special issues and computational techniques: the Bernard Wheatley Award for 2021

“…Last year saw the publication of several high-quality papers in this area, with an emphasis on the adaptation of reference ICRP models to different contexts. Thus, Kwon et al (2021) adapted the ICRP biokinetic model for iodine to make it applicable to the Korean population, whose dietary iodine intake is much higher than the global mean. Because the biokinetic models adopted by the ICRP use a substantial number of input parameters, it is important to decide which of those should be varied in adapting the model to specific populations.…”