United Nations Scientific Committee on the Effects of Atomic Radiation

ATTACHMENT A-2

THE ESTIMATION OF THYROID DOSES RESULTINGFROM THE ACCIDENT AT THE FUKUSHIMA DAIICHINUCLEAR POWER STATION AND THEIR VALIDATIONUNSCEAR 2020/2021 Report, annex B, Levels and effects of radiation exposuredue to the accident at the Fukushima Daiichi Nuclear Power Station: implicationsof information published since the UNSCEAR 2013 Report
Contents
This attachment describes the models and approaches the Committee has used to estimate theintake of radioiodine by inhalation and ingestion following the accident at the Fukushima Daiichi
Nuclear Power Station (FDNPS) and how these intakes have been transformed to effective doseand absorbed dose to various organs. A dosimetric model specific to the Japanese population,that has an iodine-rich diet, has been developed for the latter purpose. The Committee has also
undertaken an independent assessment of thyroid doses based on measurements of dose rates
near the neck for more than 1,000 people in several municipalities of Fukushima Prefecture madein March–April 2011 and compared them with those estimated by Japanese scientists. Finally,
the Committee has compared its modelled estimates of thyroid dose with those derived frommeasurements of the thyroid in order to validate the models used.
Notes
For consistency, doses in this attachment are quoted, in general, to 2 significant figures. Thisshould not be interpreted as an indication of their precision that is often much less.
The designations employed and the presentation of material in this publication do not imply theexpression of any opinion whatsoever on the part of the Secretariat of the United Nations
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Information on Uniform Resource Locators (URLs) and links to Internet sites contained in thepresent publication are provided for the convenience of the reader and are correct at the time ofissue. The United Nations takes no responsibility for the continued accuracy of that informationor for the content of any external website.

© United Nations, May 2022. All rights reserved, worldwide.
This attachment has not been formally edited.

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

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CONTENTS
I. INTRODUCTION .................................................................................................................. 5
II. THYROID DOSE ASSESSMENT IN THE UNSCEAR 2013 REPORT ............................. 5
III. NEW DATA AND INFORMATION AVAILABLE SINCE 2013....................................... 6
A. Thyroid measurements ..................................................................................................... 6
B. Ingestion of radioiodine.................................................................................................... 8
IV. JAPAN-SPECIFIC DOSE COEFFICIENTS FOR INTAKE OF RADIOIODINE............... 8
A. Stable dietary intake of iodine in Japanese diet ............................................................... 8
B. Thyroid uptake in the Japanese population ...................................................................... 9
C. International Commission on Radiological Protection dose coefficients forintake of radioiodine ....................................................................................................... 10
D. Japan-specific indicative dose coefficients for intakes of radioiodine ........................... 11
V. THYROID DOSES FROM INHALATION OF RADIOIODINE ...................................... 13
VI. THYROID DOSES FROM INGESTION OF RADIOIODINE .......................................... 13
VII.THYROID DOSES BASED ON MEASUREMENTS OF 131I IN THYROIDS...................... 15
A. Study population............................................................................................................. 15
B. Information available for the dose calculations ............................................................. 15
C. Residential history .......................................................................................................... 17
D. Measurements of 131I in the thyroids of residents of (or evacuees from)
Iitate Village, Iwaki City and Kawamata Town ............................................................. 17
E. Dosimetry model ............................................................................................................ 20
VIII.VALIDATION OF THE MODELS AND APPROACHES USED BY THE
COMMITTEE FOR ESTIMATING DOSES FROM THE INTAKE OF 131I BY
INHALATION AND INGESTION ...................................................................................... 24
A. Issues with scaling factors .............................................................................................. 25
B. Thyroid doses derived from thyroid measurements ....................................................... 26
C. Comparison of thyroid doses derived from measurements with estimatespublished by others ......................................................................................................... 27
D. Comparison of modelled and measured thyroid doses from intakes of 131I ................... 31
REFERENCES ........................................................................................................................... 35

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

I.

5INTRODUCTION

1.
This attachment summarizes the approaches and models used by the Committee, in its
UNSCEAR 2013 Report [UNSCEAR, 2014], to estimate doses to the population of Japan
resulting from intakes of radioiodine following the accident at FDNPS. Data and informationthat have since been published, or made available to the Committee, are summarized, inparticular where these have the potential to improve the validity of the estimated doses and/or
reduce their uncertainty. The Committee has used this new information to adapt the approaches
and models it had used in the UNSCEAR 2013 Report to estimate doses and the more significant
changes are described including improvements in the estimation of airborne concentrations ofradionuclides, more realistic estimates of the amount of radioiodine ingested and in the development
and use of a Japanese-specific biokinetic model for the intake of radioiodine.
2.
The Committee has also undertaken an independent assessment of thyroid doses basedon measurements of dose rates near the neck for more than 1,000 people in several municipalities
of Fukushima Prefecture made in March–April 2011 and compared them with those estimatedby Japanese scientists. The results of this comparison are summarized below. Finally, theCommittee has compared its modelled estimates of thyroid dose with those derived frommeasurements of the thyroid with the aim of validating the models and approaches used.
3.
The Committee has focused on estimating doses for four groups of geographical areas ofJapan: Group 1 included municipalities in Fukushima Prefecture from which some or all of the
population were evacuated in the days to months after the accident; Group 2 included
municipalities and parts of municipalities of Fukushima Prefecture that were not evacuated;
Group 3 included selected prefectures in eastern Japan that were neighbouring Fukushima
Prefecture (Ibaraki, Miyagi, Tochigi and Yamagata prefectures); Group 4 included all theremaining prefectures of Japan.
4.
Within these groups, the Committee has assessed doses for the three standard
International Commission on Radiological Protection (ICRP) age groups as of 2011 (1-year-old
infants, 10-year-old children and adults).

II.

THYROID DOSE ASSESSMENT IN THE UNSCEAR 2013 REPORT

5.
Assessment of doses from the intake of radioiodine into the body took account of intakes
via inhalation and ingestion of food and drinking water. The former was based on the source
term assumed in the UNSCEAR 2013 Report and an atmospheric transport, dispersion anddeposition model (ATDM) of radioiodine in particulate and gaseous forms; and the latter was
based on numerous radiation measurements of food products in a database compiled by the Foodand Agriculture Organization (FAO) and the International Atomic Energy Agency (IAEA) in
collaboration with the Ministry of Agriculture, Forestry and Fisheries (MAFF) and the Ministryof Health, Labour and Welfare (MHLW) in March–May 2011 [UNSCEAR, 2014].
6.
Two methods were used to estimate doses from the intake of radioiodine by inhalation.
The first was based on ATDM modelling of the time-dependent concentrations in air of 131I, 132I,
133
I and 132Te available on a 5 × 5 km uniform grid covering Japan. While these concentrations
were derived using the then best available source term and ATDM models, there were significant
uncertainties in their values at specific locations and times. This approach was used to estimate
doses for people from evacuated municipalities of Fukushima Prefecture.

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7.
The second was based on the estimated time-integrated concentrations of radioiodine in
air derived from measured ground deposition levels and the aggregated deposition velocity
derived from ATDM. The aggregated deposition velocities were based on ratios of ATDM
estimates of the time-integrated concentrations or radioiodine in air versus measured grounddeposition concentrations. This approach was applied to people in non-evacuated municipalities
of Fukushima Prefecture and the rest of Japan.
8.
The Committee used standard values of the age-dependent breathing rates and dosecoefficients for organ doses and for effective dose [ICRP, 1994; ICRP, 2012]. These dosecoefficients were based on a default particle size of 1 µm. The inhalation rates applied were theaverage rates over a day from the ICRP model of the respiratory tract. No allowance was madefor any possible reduction in concentrations of radioiodine in air indoors compared withthose outdoors.
9.
Doses from ingestion were based on measurements of concentrations of radioiodine infood compiled under the guidance of FAO and IAEA in collaboration with MAFF and MHLW.
The measured concentrations were combined with information on the amounts of particular
foods people ate to obtain estimated doses.
10.
Within Japan, extensive measurements were made of the concentrations of radionuclides
in different foods (terrestrial and aquatic) starting in parts of Fukushima Prefecture a few days
after the accident. These measurements were mainly intended to identify where restrictions onfood supplies were required rather than to assess the doses to different population groups. The
measurement data used were for foods as marketed, not as consumed (e.g., after culinary
preparation, etc.). Many of the measurements were at or below the limits of detection and in thesecases, it was generally assumed that the concentrations of 131I was 10 Bq/kg in each type of food,the minimum detection level. In view of the short half-life of 131I (8.02 days), all concentrations infood for this radionuclide were assumed to be zero beyond four months after the accident.
11.
There were insufficient data in the first months after the accident to adopt a fine spatial
resolution for the assessment of the doses from ingestion of radionuclides. It was assumed thatthe majority of people in Japan obtained their food from supermarkets where food is sourced
from the whole of the country.
12.
The ICRP dose coefficients applied in the 2013 Committee’s study [ICRP, 1993; ICRP,
1995] were based on generic anatomical and physiological human data and, as such, wereunlikely to have been entirely appropriate for assessing doses to the thyroid of Japanese people
because of the high iodine content of a typical Japanese diet.

III. NEW DATA AND INFORMATION AVAILABLE SINCE 2013
A.

Thyroid measurements

13.
Measurements of radioiodine in people’s thyroids provide a direct source of informationon their exposure. In March–April 2011, measurements of different quality and informativenesswere made of gamma-radiation emitted from thyroids of: (a) permanent residents of, andevacuees from municipalities in Fukushima Prefecture; (b) embassy personnel in Tokyo City
[Uyba et al., 2018]; and (c) the United States Department of Defense (DoD) and the United States
Department of Energy (DOE) personnel located in Japan [DTRA, 2012; DTRA, 2013a; DTRA,
2014].

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7

14.
In total more than 1,500 measurements of people of various age and both sexes, werecarried out by several groups of Japanese and, to a lesser extent, foreign experts. The larger
measurement campaign was conducted over the period 26 to 30 March 2011 in Iitate Village,
Iwaki City and Kawamata Town by the Support Team for Residents Affected by Nuclear
Incidents [Hosokawa et al., 2013; Kim et al., 2012; Kim et al., 2020]. In total, measurements ofdose rate at the thyroid gland were made on 1,080 children aged 1 to 15 years using handheld
dose-rate instruments. According to Hosokawa et al. [Hosokawa et al., 2013], the measurements
were performed using NaI(Tl) scintillator (1 × 1 inch) survey meters. Original calibration of thisequipment was done before the FDNPS accident and was specified, retrospectively, in Kim etal. [Kim et al., 2020]. Measured dose rates were low, in most cases lower than the backgroundlevel. Personal interviews with those measured were not conducted.
15.
Tokonami et al. reported the results of thyroid monitoring made during 12–16 April 2011
on 62 evacuees aged from 0 to 83 years from the Tsushima area of Namie Town and the coastal
area of Minamisoma City [Tokonami et al., 2012]. They detected 131I in 46 people with a 3 × 3 inch
NaI(Tl) scintillation spectrometer.
16.
The concentration of radioiodine in evacuees and short-term visitors to Fukushima
Prefecture was measured by a whole-body counter at the Nagasaki University on 15 March 2011
[Matsuda et al., 2013]. A horizontal bed-type scanner equipped with two NaI(Tl) scintillation
detectors in the upper and the lower position was used for 173 people who stayed in the
Fukushima Prefecture between 11 March and 10 April 2011. Calibration of the counting
efficiency and energy resolution was performed using a bottle manikin absorption (BOMAB)
phantom. The minimum detection level for 131I was 30 Bq. Iodine-131 was detected in
55 individuals. More information is available for 49 individuals with 131I detected in a series ofmeasurements with the same whole-body counter at Nagasaki University [Morita et al., 2013].
17.
A group of experts from the Federal Medical Biological Agency of the RussianFederation conducted, in April 2011 at the Russian Embassy in Japan, spectrometricmeasurements of 268 staff members and their families, including a few children, living in Tokyoand its suburbs [Uyba et al., 2018]. Thyroid measurements were conducted with a mobile
scintillation spectrometer. The measurement duration was two minutes, and the minimum
detection level was 100 Bq of 131I in an adult thyroid. Of those measured, three adults exceeded
the minimum detection level with up to 130 Bq of 131I in their thyroids. Each measurement was
accompanied by a personal interview focused on their residence history and dietary habits.
18.
Measurements were made, inter alia, of the thyroids of 8,238 DoD and DOE personnel(and/or their family members) who were based in Japan or nearby at the time of the accident, or
on-board ships in the general vicinity [DTRA, 2012; DTRA, 2014]. Of these, 238 individuals
had measured levels (i.e., above minimum detection levels) of radioiodine in their thyroids. Nine
hundred and forty-four people were measured using fixed scanners at naval bases on the west
coast of the United States of America and, of these, 104 had measured concentrations of 131I intheir thyroids in the range of 37 to 296 Bq. The average absorbed dose to the thyroid for the
238 individuals with measured levels of radioiodine in the thyroid was about 0.7 mGy [DTRA,
2013b]. Deterministic and probabilistic assessments [DTRA, 2012; DTRA, 2013a] have been
made of doses from intakes of radionuclides, with the former being deliberately conservative.
19.
The Committee has also made use, to varying extents, of results of thyroid measurement
published in the peer-reviewed literature for model validation and further elaboration.

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B.

Ingestion of radioiodine

20.
Murakami and Oki have undertaken a comprehensive assessment of the ingestion ofradionuclides during the first year after the FDNPS accident by people of various ages residingin the cities of Fukushima, Osaka and Tokyo [Murakami and Oki, 2014]. They used data fromnational food monitoring. Food and drinking water were classified into 18 categories, which
included rice and other cereals, vegetables and fruits, dairy and meat products, fish, etc. The
consumption rates of food and water by people of different sex and age were taken from national
statistics. In contrast to analyses made by international organizations [UNSCEAR, 2014; WHO,2012], Murakami and Oki carefully considered the particularities of regional trade in Japan andthe effects of countermeasures. For Fukushima City, two cases were considered: Case 1 –purchase of all products on the market; and Case 2 – consumption of locally produced vegetables(e.g., by agricultural workers comprising about 4% of the population) and purchase of otherproducts on the markets. By modelling, the authors found reasonable agreement withmeasurements of radiocaesium in diet; similar validation for radioiodine was not/could not be
performed.
21.
The doses decreased significantly (see table A-2.1) with increasing distance fromFDNPS: Fukushima > Tokyo > Osaka. The thyroid dose for children is about three times higher
than that for adults, mainly due to the consumption of drinking water and liquid foods (milk,etc.). For residents of Fukushima Prefecture who were assumed to have consumed local
vegetables (agricultural workers comprising about 5% of the population), the average dose wasabout three times higher than that of other residents. In general, according to Murakami andOki’s estimates, the dose from ingestion of 131I in food and drinking water was an order ofmagnitude lower than that estimated by the Committee [UNSCEAR, 2014; WHO, 2012].
Table A-2.1. Estimated doses to adults and children of various ages living in different locations,from the ingestion of 131I in food and drinking water in the first year ([Murakami and Oki, 2014],
International Commission on Radiological Protection dose coefficients)
Absorbed dose to thyroid a (mGy)
Location

Effective dose a (mSv)

Adults

7–12
years old

1–6
years old

Adults

7–12
years old

1–6
years old

Fukushima City (market)

0.82

2.1

2.6

0.034

0.090

0.11

Fukushima City (locallygrown vegetables)

2.6

5.8

6.9

0.11

0.24

0.28

Tokyo City

0.22

0.38

0.49

0.009

0.016

0.020

Osaka City

0.016

0.032

0.040

0.001

0.001

0.002

a

The doses reported by Murakami and Oki were estimated using generally applicable dose coefficients for the intake of radioiodine
recommended by ICRP; they would decrease by a factor of about two had Japanese-specific dose coefficients been used (see section IV).

IV. JAPAN-SPECIFIC DOSE COEFFICIENTS FOR INTAKE OF
RADIOIODINE
A.

Stable dietary intake of iodine in Japanese diet

22.
The Japanese population has an iodine-rich diet [Katagiri et al., 2015; Leggett, 2010;
Nagataki et al., 1967; Zimmermann et al., 2004; Zimmermann et al., 2005]. Stable iodine comesmainly from seafood, particularly algae, which is a traditional component of the Japanese diet.
Typically, kelp contributes up to 90% of the total iodine intake in Japan [Katagiri et al., 2015].
In the review of Zava and Zava [Zava and Zava, 2011] the average Japanese iodine intake wasANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

9

estimated to be about 1,000–3,000 μg/d, which may result in suppression of iodine accumulationby the thyroid gland. Tables A-2.2 and A-2.3 summarize Japan-specific data on the dietary iodine
intake rate, Y (μg/d), and decay-corrected percentage thyroid uptake U(%), of ingested iodine at
24 hours. The reference ICRP biokinetic model [ICRP, 1989] assumes a moderate level of
dietary intake of stable iodine at about 200 μg/d for adults [ICRP, 1975].
Table A-2.2. Dietary intake rate, Y, of stable iodine (range, mean and standard deviation) andfractional thyroid uptake Ua (range and mean) measured in residents of Japan
Number of individuals

Y range(μg/d)

Y mean(μg/d)YSD(μg/d)

U range(%)

U mean(%)

4 adults

878–1 690

1 132

n/a

10.2–15.8

12.5[Nagataki et al., 1967]

7 adults

n/a

1 523

356

9.5–26.6

16.7[Ohtaki et al., 1967]

2 adults

13 760–17 300

15 540n/a

2.6–7.5

5.1[Nagataki et al., 1967]

302
6–12-year-old children
Central Hokkaido≈50–14 000b

≈300b

n/a

n/a

n/a

[Zimmermann et al.,
2005]

280
6–12-year-old children
Coastal Hokkaido≈40–11 000b

≈700b

n/a

n/a

n/a

[Zimmermann et al.,2005]

54 adults≈40–8 700

≈1 000≈2 000n/an/a[IAEA, 2008]

390 adults

See table A-2.3[Katagiri et al., 2015]

Not specified

12.8 ± 5.7

15 adults
a
b

n/a

n/a

n/a

Reference

9.1–26

16.1[Kunii et al., 2012][Kusuhara and Maeda,
2017]

Decay-corrected fractional thyroid uptake, U, of ingested radioiodine at 24 hours.
Estimated from concentrations of stable iodine in urine in an assumption of the urinary excretion rate of about 1 L/d.

Table A-2.3. Intake rate of stable iodine in the various diets of Japanese adults[Katagiri et al., 2015]
Percentage of men (number)

Percentage of women (number)

Iodine intake,Y

Cluster I
Rice andvegetables(n=101)Cluster II
Meat,
non-Japanese noodles
and sugar-sweetened
beverages (n=34)

Cluster III
Fish, Japanese
noodles andalcohol(n=60)

Cluster I
Rice andvegetables(n=22)

Cluster II
Fish andJapanese
noodles(n=33)

Cluster III
Bread andnon-Japanese
noodles(n=140)<95 μg/d

5.9 (6)23.5 (8)1.7 (1)

13.6 (3)

6.1 (2)

18.6 (26)>3 000 μg/d22.8 (23)

5.9 (2)

18.3 (11)50.0 (11)36.4 (12)13.6 (19)23.
Generally, the intake rate of stable iodine for Japanese people is substantially higher thanin countries with a Western pattern diet [ICRP, 1975]. A significant inter-individual andinterregional variability of the dietary iodine intake is also observed in Japan. For some Japanesepeople, a low iodine intake can be associated with the Western pattern diet.
B.

Thyroid uptake in the Japanese population

24.
Some values of the decay-corrected percentage thyroid uptake, U(%), of ingested
radioiodine at 24 hours are given in table A-2.2. Figure A-2.I from Kusuhara and Maeda[Kusuhara and Maeda, 2017] summarizes the results of Japanese studies conducted during 1958–
2013. All recent data demonstrate that U-values in Japan are typically lower than the reference
ICRP value of 30%. In a recent study, Kusuhara and Maeda [Kusuhara and Maeda, 2017]

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ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

obtained a mean U = 16.1 ± 5.4% for 15 Japanese euthyroid male subjects from Nagasaki, and asimilar study in Tokyo resulted in the value of U = 12.8 ± 5.7% [Kunii et al., 2012].
Figure A-2.I. Fractional thyroid uptake, U(%), of radioiodine by Japanese adults [Kusuhara and
Maeda, 2017]

C.

International Commission on Radiological Protection dosecoefficients for intake of radioiodine

25.
In the UNSCEAR 2013 Report, the Committee estimated doses to the thyroid gland basedon ICRP reference dose coefficients [ICRP, 1993; ICRP, 1995]. These age-dependent dosecoefficients were derived by ICRP with the use of a reference 3-compartmental iodine biokinetic
model [ICRP, 1989; ICRP, 1993].
26.
The ICRP reference biokinetic and dosimetric models, and the associated set of reference
dose coefficients, were primarily intended for applications in routine radiation protection, suchas optimization of protection and demonstration of compliance. For these reasons, the parametervalues of ICRP reference models are generalized and based on worldwide-average data. The
reference ICRP dose coefficients for internal exposure are expressed in terms of protection
quantities, i.e., committed effective dose and committed equivalent doses to organs or tissues of
the ICRP Reference Person [ICRP, 2001].
27.
The simplified model structure and fixed value of 24-hour fractional thyroid uptake of
U = 30% (related to the reference dietary intake of stable iodine at the level of about 150 μg/d)
results in unrealistic dose estimates for situations where the actual dietary intake of iodine issubstantially lower or higher than the reference level.
28.
In 2017, ICRP adopted a new model of iodine biokinetics in adults [ICRP, 2017] that isbased on the model of Leggett [Leggett, 2010]. The model, similar to the model of Berkovski[Berkovski, 2002], provides an improved description of the short-term biokinetic processes andpermits more precise assessments of exposure to short-lived isotopes of iodine, namely 132I, 133I

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

11and exposure to 132Te that has a radioactive progeny 132I. The structure of the model is presented
in figure A-2.II, and its reference parameter values for workers are given in the ICRP Publication
137 [ICRP, 2017]. The new age-dependent version of the model is under development [ICRP, 2020].
Figure A-2.II. The structure of the new International Commission on Radiological Protection
iodine biokinetic model for adults [ICRP, 2017]

D.

Japan-specific indicative dose coefficients for intakes of radioiodine

29.
The default parameter values of the model [Leggett, 2010] are based on the following
values for dietary intake of stable iodine: 130 μg/d for an adult female, 190 μg/d for an adultmale, and 160 μg/d as a reference sex-averaged value. However, the key advantage of the model
is its capability to account for a non-reference level of dietary intake of stable iodine. The thyroid
responds to changes in the level of dietary stable iodine intake by modification of its rate ofiodide uptake from blood plasma. The detailed description of the regulation of the thyroid uptake
and secretion of thyroid hormones is given elsewhere [Luster et al., 2019] whereas the paper[Leggett, 2010] includes guideline and parameter values for simulation of the influence of elevatedlevels of stable iodine in the diet. Age-specific data demonstrate that there is no pronounced
dependence of the fractional thyroid uptake U with age [Fields et al., 1957; ICRP, 2020].
30.
The Committee developed the new model to derive population-specific indicative dosecoefficients for various types of Japanese diet with different content of stable iodine that
determines the fractional thyroid uptake, U. The values of the indicative dose coefficients “doseper exposure (time-integrated air concentration)”, specifically “organ absorbed dose per
exposure, Gy per (Bq s/m3)” and “effective dose per exposure, Sv per (Bq s/m3)” were calculated
for inhalation of various physico-chemical forms of 131I, 132I, 133I and 132Te and three types of thediet: typical Japanese diet (U = 15%), kelp-rich diet (U = 5%), and a Western pattern diet (witha reference value of U of about 30%) that is popular among some groups of the Japanese
population. The dose coefficients were developed for the thyroid, red bone marrow, female

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ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

breast and colon as well as for effective dose from inhalation of aerosols, Type F, activity medianaerodynamic diameter (AMAD) = 1 µm, methyl iodide and elemental iodine.
31.
The indicative dose coefficients are provided for a non-lactating adult female, adult male,
10-year-old child and 1-year-old infant.
32.
Additionally, the dose coefficients for in utero exposure are given for acute inhalationand ingestion at the 35th week of pregnancy in terms of the fetus absorbed dose and fetus
effective dose per maternal exposure. These can be considered as the upper bounds of thyroid
dose to the fetus for maternal intake of radioiodine by inhalation or ingestion (i.e., intakes atother times during pregnancy would result in lower dose coefficients). For intakes at other times
during pregnancy, in utero doses can be estimated using the model and data of ICRP [ICRP, 2001].
33.
The model in ICRP Publication 88 takes account of the fetal thyroid gland not
substantially concentrating iodine prior to the 10th week of pregnancy. The ratios of the dosecoefficients for inhalation or ingestion of 131I at the 10th, 15th and 25th weeks of pregnancy tothat for intake at the 35th week are 0.003, 0.22 and 0.62, respectively [ICRP, 2001]. Based onlinear interpolation, the average dose to the thyroid gland of fetuses between the 10th and 40th
weeks of pregnancy at the time of the accident (i.e., those born between mid-March and midOctober 2011) from the intake of 131I is 0.47 times the dose estimated for intake by a child inutero at the 35th week of pregnancy.
34.
Calculations were performed with the IDSS computer code [Berkovski et al., 1998;
Berkovski et al., 2007]: this implements the biokinetic models described above, the ICRP
dosimetric models [ICRP, 1989; ICRP, 1994; ICRP, 2001], and uses ICRP reference masses oftarget organs and tissues [ICRP, 2002] (see table A-2.4) and the definition of effective dose in
ICRP Publication 103 [ICRP, 2007].
Table A-2.4. Mass of the thyroid gland used in calculations of Japan-specific indicative dosecoefficients [ICRP, 2002]Age

1-year-old infant

10-year-old child

Adult

Sex

Both

Both

M

F

Thyroid mass (g)

1.8

7.9

20

17

35.
The inter-individual variability of dietary habits, biokinetics, anatomy and organ masses
results in a considerable variation of individual-specific doses among people of the same age andsex. Therefore, the Japan-specific dose coefficients should be regarded as indicators of the levelof dose per exposure among people with differing types of diet, rather than exact values that canbe attributed to a specific age, sex and diet.
36.
Japan-specific indicative dose coefficients are presented in attachment A-4 for intake byadults (male and female), 10-year-old children, 1-year-old infants for various levels of dietaryintake of stable iodine, and for those in utero at the 35th week of pregnancy. The dose coefficientswere developed both for inhalation and ingestion of radioiodine. For inhalation, dose coefficientsfor intake of 131I, 132I, 133I and 132Te in various physical and chemical forms (aerosol with AMAD
1 µm, Type F, elemental iodine and methyl iodide) are given for absorbed doses per unit
exposure in various organs (thyroid, bone marrow, colon and breast), Gy per (Bq s/m3), andeffective dose per unit exposure, Sv per (Bq s/m3). For ingestion, dose coefficients are given for
intake of 131I in a soluble form for absorbed doses in various organs and effective dose.

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

13

37.
In summary, the Japan-specific dose coefficients used by the Committee for intake of 131I
in various physical and chemical forms are lower by factors in the range of 1.8 to 2.3 than thoserecommended by ICRP for generic use worldwide [ICRP, 1993; ICRP, 1995]; the reduction
varies with age at exposure, sex and diet.

V. THYROID DOSES FROM INHALATION OF RADIOIODINE
38.
The Committee has estimated doses to the population of Japan from inhalation ofradioiodine based on an assumed source term and models to describe how released material isdispersed in, and deposited from, the atmosphere (see attachments A-9 and A-10). The 5%, mean
and 95% thyroid doses from inhalation of radioiodine and other radionuclides by adults andchildren, aged 10 and 1, are presented in attachment A-18 for evacuees from municipalities
wholly or partially evacuated in Fukushima Prefecture (Group 1), and in attachment A-14 forresidents of each of the municipalities or parts of municipalities in Fukushima Prefecture thatwere not evacuated (Group 2), for four neighbouring prefectures (Group 3) and for the remaining
prefectures (Group 4). Estimates are also given in attachments A-14 and A-18 of average doses
to the fetal thyroid for fetus in utero between the 10th and 40th weeks of pregnancy at the timeof the accident (i.e., those born in the 30 weeks following the accident).
39.
The inhalation doses varied widely within Fukushima Prefecture and beyond and were
influenced, inter alia, by the prevailing meteorological conditions that determined where andhow the released material was dispersed.

VI. THYROID DOSES FROM INGESTION OF RADIOIODINE
40.
The Committee has based its estimates of doses from ingestion of radioiodine on the
study undertaken by Murakami and Oki [Murakami and Oki, 2014] that took account ofmonitored levels of radioiodine in food and drinking water, food supply and distribution
practices, losses in food preparation and countermeasures. Murakami and Oki estimated doses
for three cities: Fukushima City, Osaka City and Tokyo City (or Metropolitan Area). The
Committee has assumed that the ingestion doses estimated by Murakami and Oki for Fukushima
City are applicable to the whole of Fukushima Prefecture; this was judged to be a reasonableapproximation given food supply and distribution practices in Japan.
41.
The Committee’s estimates of thyroid and effective doses are summarized in table A-2.5
for Fukushima Prefecture and other prefectures. The tabulated doses differ from those reported by
Murakami and Oki because account has been taken of Japan-specific dose coefficients for theingestion of radioiodine that are more appropriate for people with a typical Japanese diet (seesection IV of this attachment); the use of Japanese-specific dose coefficients resulted in the
reduction of the doses reported by Murakami and Oki by a factor of about two. The doses in table
A-2.5 are more than an order of magnitude lower than the Committee’s estimates in its UNSCEAR
2013 Report. The most likely causes of the overestimate were twofold; firstly, the use by theCommittee of a database compiled by FAO and IAEA [UNSCEAR, 2014] of monitored levels infood that may have been biased towards identifying samples whose levels may have exceeded
limits imposed by the Japanese authorities; and, secondly, the attribution of the minimum detectionlevel of 10 Bq/kg of 131I to all samples with measurements beneath that level.
42.
The Committee estimated thyroid and effective doses in other prefectures using largely
the same approach as it used in the UNSCEAR 2013 Report [UNSCEAR, 2014]. The doses were
estimated from monitored levels of radioiodine in food sampled in markets across the whole of

14

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Japan (i.e., the database compiled by FAO and IAEA). The dose in a given prefecture wasderived from that in Fukushima Prefecture by scaling the ratio of the monitored levels ofradioiodine in food in that prefecture relative to that in Fukushima Prefecture; the ratios forGroup 3 and Group 4 prefectures were 0.27 and 0.075, respectively. Notwithstanding thereservations expressed above regarding the use of the database compiled by FAO and IAEA for
estimating absolute values of dose from intake by ingestion, the Committee has judged that therelative levels in (or ratios between) each prefecture should be robust.
Table A-2.5. Estimated thyroid and effective doses to adults, children and infants, living indifferent locations, from the ingestion of 131I in food and drinking water in the first year (basedon reference [Murakami and Oki, 2014] but using Japan-specific dose coefficients)
Prefecture
group

Absorbed dose to thyroid a (mGy)

Effective dose a (mSv)

Location
Adults10-year old

1-year old

Adults10-year old

1-year old

2

Fukushima
Prefecture

0.41

0.94

1.14

0.017

0.039

0.047

3

Neighbouring
prefectures

0.11

0.25

0.31

0.005

0.010

0.013

4

Distant
prefectures

0.031

0.071

0.086

0.001

0.003

0.004

a

Estimates are not tabulated for doses to the fetus. Conservative estimates of fetal effective and thyroid doses would be factors of about 2.3 and1.8 times greater, respectively, than the corresponding tabulated adult doses.

43.
The Committee, in applying the Japan-specific dose coefficients, has taken the doses
from table A-2.1 for the 7–12-year age group and assigned them to a 10-year-old child and,similarly, assigned doses for the 1–6-year age group to a 1-year-old infant. In the latter case, thedoses to the 1-year-old infant may have been underestimated by up to a few tens of per cent as aresult of significant variation in the thyroid dose coefficient at very young ages.
44.
Based on Murakami and Oki [Murakami and Oki, 2014] and expert judgement, theconfidence intervals (5–95%) for the thyroid and effective doses in table A-2.5 have been
estimated to be 0.3 and 3.0 times the doses tabulated.
45.
Absorbed doses in red bone marrow, breast and colon from ingestion of 131I have beenassessed (see table A-2.6) from the thyroid doses by the ratio of dose coefficient for a particularorgan to that for the thyroid for each age, see attachment A-4.
46.
Estimates have also been made by the Committee of average doses to the fetus of children
in utero between the 10th and 40th weeks of pregnancy at the time of the accident (i.e., thoseborn in the 30 weeks following the accident) and can be found in attachments A-14 and A-18.
Table A-2.6. Ratio of dose coefficients to that for the thyroid for ingestion of 131I
Ratio of dose coefficients (unitless)
Age
Effective

ThyroidRed bone marrow

BreastColon

1 year

0.040

1.00

3.0E-4

1.6E-4

2.3E-410 years

0.041

1.00

3.5E-4

1.7E-4

2.6E-4

1.00

6.5E-4

2.3E-4

3.2E-4

1.00

6.5E-4

3.7E-4

2.7E-4Adult male
0.041
Adult female

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

15

VII. THYROID DOSES BASED ON MEASUREMENTS OF 131I IN
THYROIDS
A.
47.

Study population

The study population comprised in total 1,146 Japanese individuals:− 1,080 individuals aged up to 15 years who were measured for radioiodine in the thyroid
gland from 26 March 2011 through 30 March 2011 in three municipalities in Fukushima
Prefecture: Iitate Village, Iwaki City and Kawamata Town [Kim et al., 2020];− 3 adults in Tokai Village [Kurihara et al., 2016];− 1 adult from Tamura [Uchiyama et al., 2015];− 45 individuals from Minamisoma City and 17 from Namie Town [Tokonami et al., 2012].

48.
The measurements of thyroids in personnel of the Russian Embassy in Tokyo [Uyba etal., 2018] were not included in the study population owing to the very small number ofmeasurements that were above the minimum detection level (3 out of 168). The measurementsof thyroids of DoD and DOE personnel were not included in the study because the focus was on
exposures in the Japanese population.
B.

Information available for the dose calculations

49.
Table A-2.7 summarizes the availability of information that should be used in calculating
absorbed doses in the thyroids of those measured.
Table A-2.7. Availability of information that should be used to calculate the absorbed doses inthe thyroids of those measured
Availability of information for measurements
Information[Kim et al.,2020]

[Kurihara
et al., 2016][Uchiyama
et al., 2015][Tokonami
et al., 2012]

Direct thyroid measurement
Number of persons

1 080

3

1

62

Results of direct thyroid measurement

+

+

+

+

Results of measurement of background

+

–

–

–

Characteristics of the device used to measure the 131I
in the thyroid

+

–

–

–

+

+

+

Environmental radiation data
Daily concentration of 131I in ground-level air at
location/s where exposure occurred+50.
The general scheme for estimating thyroid doses from direct thyroid measurements isshown in figure A-2.III. Thyroid doses were estimated using input data specific to eachindividual (direct thyroid measurement) and ecological data (131I concentrations in ground-level
air at the location/s where the exposure occurred). Ecological and biokinetic models were used
to reconstruct the transport of 131I in air to the human thyroid through intake by inhalation. Thesemodels were used to calculate: (a) the time-integrated activity of 131I in the thyroid, from which
the “ecological dose” was derived; and (b) the activity of 131I in the thyroid at the time of thedirect thyroid measurement, called the “ecological” 131I activity in the thyroid. To calculate the16

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

“instrumental” or realistic thyroid dose, the ecological dose was scaled by so-called “scaling
factor” that is the ratio of ecological 131I activity in the thyroid at the time of measurement to 131I
activity in the thyroid derived from the direct thyroid measurement. All steps of dose calculations
are discussed in the following sections.
Figure A-2.III. The general scheme of thyroid dose calculation using direct thyroid measurement

51.
Unfortunately, important information for each measured person (i.e., that could beobtained by means of a personal interview) was not available, such as: changing clothes andwashing before measurements; residential history from the time of the accident until the date ofmeasurement; consumption of locally produced foodstuffs and drinking water, administration of
stable iodine to block the uptake of radioiodine to the thyroid.
52.
As personal interviews with those measured were not conducted, the following assumptions
were made:− There was no consumption of locally produced foodstuffs that may have contained 131I,
i.e., intakes of 131I only by inhalation and drinking of tap water were considered;− There was no administration of stable iodine among measured individuals to block the
uptake of ingested or inhaled radioiodine to the thyroid.

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

C.

17

Residential history

53.
The residential history was not available for the measured individuals, so the following
assumptions were made:(a) Iwaki City, Kawamata Town: permanent residence at the location where a measurement
was made, as assumed by Kim et al. [Kim et al., 2020];(b) Iitate Village: four scenarios of evacuation and residence were assumed according to
Ohba et al. [Ohba et al., 2020]:− IT1: evacuation to Koriyama City on 16 March 2011 (30% of population);− IT2: evacuation to Fukushima City via Kawamata Town on 15 March 2011 and thento Aizu on 21 March 2011 (24% of population);− IT3: evacuation to distant areas on 19 March 2011 (25% of population); and− IT4: permanent residence at Iitate Village (21% of population);(c) Tokai Village and Tamura Town: permanent residence at the location where a measurement
was made;(d) Minamisoma City: two groups with low and high levels of 131I in the thyroid were foundreflecting two scenarios of residence according to Kawai et al. [Kawai et al., 2018]:− Minamisoma 1: evacuation to Date City on 15 March 2011 (persons with low levelsof 131I in the thyroid in the range from 0.006 to 0.13 kBq on 16 April 2011); and− Minamisoma 2: evacuation to Niigata Prefecture on 23 March 2011 (persons withhigh levels of 131I in the thyroid in the range from 0.13 to 1.1 kBq on 16 April 2011);(e) Namie Town: two groups with low and high levels of 131I in the thyroid were foundreflecting two scenarios of residence according to Kawai et al. [Kawai et al., 2018]:− Namie 1: evacuation to Nihonmatsu City on 15 March 2011 (persons with low levelsof 131I in the thyroid in the range from 0.044 to 0.093 kBq on 13–15 April 2011); and− Namie 2: permanent residence at the location where a measurement was made wasassumed (persons with high levels of 131I in the thyroid in the range from 0.38 to
1.5 kBq on 13–14 April 2011).
D.

Measurements of 131I in the thyroids of residents of (or evacuees from)
Iitate Village, Iwaki City and Kawamata Town

54.
The number of individuals measured in each municipality are summarized in table A-2.8
together with the date when the measurements were made.
Table A-2.8. Distribution of 1,080 individuals measured by date and location
Date in 2011

Iitate Village

Iwaki City

Kawamata Town

Total

26 March

46

46

27 March

88

88

28 March

219

219

29 March

272

272

156

455

647

1 080

30 March

299

Total

299

134

18

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

55.
According to Hosokawa et al. [Hosokawa et al., 2013], the thyroid measurements were
performed using NaI(Tl) scintillator (25.4 mm × 25.4 mm survey meters TCS-171 and TCS-172(Hitachi-Aloka Medical, Ltd.). The operators recorded results of measurements as ambient dose
equivalent rates (referred to hereafter as dose rates) in units of μSv/h for each measured
individual as follows: the average dose rate from 3 measurements (duration of 30 seconds each)done in geometry “detector against thyroid”; and measurements of background but it was unclear
where these were made. Kim et al. [Kim et al., 2020] indicate that background measurements
were made on another part of the body of measured individuals without specifying whether it
was against the shoulder, stomach or other parts of the body.
1.

Background radiation in the room where measurements were performed

56.
When the background radiation in the room was measured during the direct thyroid
measurements, the net exposure rate was calculated as:
𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ) = 𝑃𝑃𝑚𝑚 (𝑡𝑡𝑚𝑚 ) − 𝑃𝑃𝑏𝑏𝑏𝑏 (𝑡𝑡𝑚𝑚 )(A-2.1)

where 𝑃𝑃𝑚𝑚 (𝑡𝑡𝑚𝑚 ) is the dose rate measured near the thyroid gland (μSv/h); 𝑃𝑃𝑏𝑏𝑏𝑏 (𝑡𝑡𝑚𝑚 ) is the
background radiation (μSv/h) in the room where the measurements were performed; and𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ) is the net dose rate (μSv/h).
2.

Lower limits of exposure rate57.
For 598 (55.4% of the total) of the 1,080 individuals measured, the dose rate measured
near the thyroid was recorded as equal to or less than the background radiation measurement. In
order to prevent the use of these values of net dose rate, 𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ) , for the direct thyroid
measurements, such values, when they occurred, were replaced with lower limits of dose rate.
The values of lower limits of dose rate depend on the type of device and on the magnitude of thedose rate due to background radiation in the room. The lower limits of dose rate (μSv/h) were
calculated using the following equation [ISO, 2000]:𝑃𝑃𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 (𝑡𝑡𝑚𝑚 ) =𝑡𝑡𝑝𝑝2
8 ∙ 𝑘𝑘 ∙ 𝑃𝑃𝑏𝑏𝑏𝑏 (𝑡𝑡𝑚𝑚 ) ∙ 𝑇𝑇 ∙ 𝛿𝛿 2
∙ (1 + �1 +)2 ∙ 𝑘𝑘 ∙ 𝑇𝑇 ∙ 𝛿𝛿 2
𝑡𝑡𝑝𝑝2

(A-2.2)where 𝑡𝑡𝑝𝑝2 = 1.96 is the Student statistics; 𝑘𝑘 is the scale coefficient for the device from impulse toscale reading and is equal to 460 (counts/s per μSv/h) for the TCS-172 device (derived from [Suhand Kurihara, 2013]); 𝑇𝑇 =30 s is the duration of measurement; δ=1 is the relative error ofmeasurement (unitless).
58.
The lower limits of dose rate values, which were assigned to 598 measured individuals,
vary from 0.006 μSv/h to 0.011 μSv/h.
(a)Contribution to the measured signal from radionuclides on the body and clothes ofmeasured people

59.
Ohba et al. [Ohba et al., 2017] addressed the issue of radionuclides on the body andclothes of those evacuated from a 20-km zone around FDNPS who were measured between 12
and 17 March 2011. However, the Committee did not make any allowance for this in its
assessment as, according to Hosokawa et al. [Hosokawa et al., 2013] it was assumed, based on

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

19

monitoring before direct thyroid measurements, that there was no surface contamination of the
body and clothes of measured individuals.
(b)

Dose rate used to calculate 131I in the thyroid60.
The dose rates used by the Committee in estimating the levels of 131I in the thyroid arecompared in figure A-2.IV with those of Japanese scientists. The use of the lower limits of dose
rate concept eliminates zero values of net exposure rate, 𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ). However, around 80% (858from 1,080) of the measurements resulted in values of net exposure rate equal to or less than
0.01 μSv/h.
Figure A-2.IV. Comparison of dose rates obtained in this study with those obtained by
Hosokawa et al. [Hosokawa et al., 2013](c)

Iodine-131 in the thyroid

61.
Assuming that there were no radionuclides on the surface of the body and clothes ofmeasured individuals, the net dose rate, 𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ), is only due to the 131I in the thyroid of thesubject at the time of the measurement. The relationship between 𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ) and the 131I in the
thyroid is as follows:
𝑄𝑄𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 (𝑡𝑡𝑚𝑚 ) = 𝑃𝑃𝑛𝑛𝑛𝑛𝑛𝑛 (𝑡𝑡𝑚𝑚 ) ∙ 𝐶𝐶𝐶𝐶𝑘𝑘(A-2.3)where 𝑄𝑄𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 (𝑡𝑡𝑚𝑚 ) is the activity of 131I measured in the thyroid (kBq); 𝐶𝐶𝐶𝐶𝑘𝑘 is the device
calibration coefficient for a person of age k (kBq per μSv/h).

20

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

(d)

Calibration coefficients for scintillator survey meter TCS-172

62.
The direct measurements of 131I in the thyroids of people affected by the accident at FDNPS
were made using devices not specifically designed for this purpose. Therefore, Japanese scientists
needed to estimate age-dependent calibration factors for 131I for the survey meter TCS-172.
63.
Calibration coefficients were obtained using Monte Carlo simulations of the NaI(Tl)survey meter and age-specific phantoms modified by Ulanovsky and Eckerman [Ulanovsky and
Eckerman, 1998] and have been published by Kim et al. [Kim et al., 2020]. Table A-2.9 gives
values of age-dependent calibration coefficients, 𝐶𝐶𝐶𝐶𝑘𝑘 , obtained by Kim et al. [Kim et al., 2020]
for different distances between detector and the neck of the measured person as well as values
used by Kim et al. [Kim et al., 2020] for estimates of the activity of 131I in the thyroid. To beconsistent with the analysis of Kim et al. [Kim et al., 2020], the same values of 𝐶𝐶𝐶𝐶𝑘𝑘 have beenused by the Committee.
Table A-2.9. Age-dependent calibration coefficients, 𝑪𝑪𝑪𝑪𝒌𝒌 , (kBq per μSv/h) obtained by Kim et al.
[Kim et al., 2020]
Age
0

𝐶𝐶𝐶𝐶𝑘𝑘 (kBq per μSv/h)Distance between detector and the neck (mm)510𝐶𝐶𝐶𝐶𝑘𝑘 (kBq per μSv/h)
Used by Kim et al. [Kim et al.,2020] and by the Committee

Newborn

11.0

15.2

20.0

16.8

1 year

12.4

16.7

21.7

18.5

5 years

13.8

18.4

23.6

20.1

10 years

17.9

22.9

28.7

25.4

15 years

21.1

26.6

32.7

29.4

20 years (adults)

24.2

29.8

36.0

33.0

E.

Dosimetry model

64.
The ecological and biokinetic models were used to reconstruct the transport of 131I fromthe environment to the thyroids of people from intakes by inhalation and ingestion. The models
used for this purpose have been described in sections IV, V and VI for intakes by the respective
pathways, i.e., estimation of the time-integrated concentration of 131I in the thyroid, from which
the so-called “ecological dose” is derived, and the activity of 131I in the thyroid at the time of its
measurement, called the “ecological” activity of 131I in the thyroid. To calculate the so-called“instrumental” or realistic thyroid dose, the “ecological dose” has been scaled by so-called“scaling factor” that is the ratio of the activity of 131I in the thyroid derived from the direct thyroid
measurement to the ecological 131I activity in the thyroid at the time of measurement.
1.

Ecological dose65.
The following equation was used to calculate “ecological” thyroid doses due to 131I intake(see figure A-2.III):∞13.82 ∙ 𝐸𝐸𝑡𝑡ℎ,𝑘𝑘
𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 =∙ � 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 (𝑡𝑡)𝑑𝑑𝑑𝑑
𝑚𝑚𝑡𝑡ℎ,𝑘𝑘0(A-2.4)

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

21

where 𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 is the thyroid dose due to 131I intake (mGy); 13.82 is a unit conversion factor((Bq/kg)(g/kg)(J/MeV)(s/d)(mGy/Gy)); 𝐸𝐸𝑡𝑡ℎ,𝑘𝑘 is the mean energy absorbed in the thyroid per
decay of 131I in the thyroid [Mowlavi et al., 2011] (MeV); 𝑚𝑚𝑡𝑡ℎ,𝑘𝑘 is the sex-specific thyroid massfor person of age k [ICRP, 2002](g); and 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 (𝑡𝑡) is the variation with time of ecological activityof 131I in the thyroid (Bq) that is described by equations A-2.5 to A-2.7.
2.

Ecological activity of 131I in the thyroid66.
Two pathways of 131I intake were considered in this study: inhalation of air and ingestionof tap water containing radioiodine.
67.

The activity of 131I in the thyroid at day t from inhalation was calculated as:

𝐼𝐼−131
𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (𝑡𝑡) = 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (𝑡𝑡 − 1) ∙ 𝑒𝑒 −(𝜆𝜆𝑡𝑡ℎ,𝑘𝑘 +𝜆𝜆𝑟𝑟,𝐼𝐼−131 )∙∆𝑡𝑡 + 𝐶𝐶𝑎𝑎𝑎𝑎𝑎𝑎(𝑡𝑡) ∙ 𝐵𝐵𝑘𝑘 ∙ 𝐹𝐹𝑖𝑖𝑖𝑖 ∙ 𝑤𝑤𝑖𝑖𝑖𝑖ℎ ∙ 𝑤𝑤𝑡𝑡ℎ(A-2.5)where 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (𝑡𝑡) is the ecological activity of 131I in the thyroid due to inhalation (kBq) at day twith initial condition of 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (0) = 0; 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (𝑡𝑡 − 1) is the ecological activity of 131I in the
𝐼𝐼−131thyroid at day t-1 (kBq); Δ𝑡𝑡 = 1 d is the calculation step; 𝐶𝐶𝑎𝑎𝑎𝑎𝑎𝑎(𝑡𝑡) is the time-integrated
concentration of 131I in air at the location of residence during the day t ((kBq d)/m3); 𝐵𝐵𝑘𝑘 is thedaily-average breathing rate for a person of age k [ICRP, 2002] (m3/d); 𝐹𝐹𝑖𝑖𝑖𝑖 is the ratio of theactivity of 131I inhaled in air during the day while staying indoors and outdoors to the activity of131
I inhaled while staying outdoors for the entire day (determined by the time spent indoors andthe reduction in the concentration of 131I air while there in comparison with being outdoors (seetable A-2.10)) – the reduction in the concentration of 131I in air indoors was assumed to be 0.5;
𝑤𝑤𝑖𝑖𝑖𝑖ℎ = 0.66 is the fraction of inhaled iodine transferred to blood [ICRP, 1995] (unitless);
𝑤𝑤𝑡𝑡ℎ = 0.15 is the Japan-specific fraction of iodine uptake by the thyroid (unitless).
68.

The activity of 131I in the thyroid at day t due to ingestion of tap water was calculated as:

𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (𝑡𝑡) = 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (𝑡𝑡 − 1) ∙ 𝑒𝑒 −(𝜆𝜆𝑡𝑡ℎ,𝑘𝑘+𝜆𝜆𝑟𝑟,𝐼𝐼−131 )∙∆𝑡𝑡 + 𝐷𝐷𝐷𝐷 𝐼𝐼−131 (𝑡𝑡) ∙ 𝑉𝑉𝐷𝐷𝐷𝐷,𝑘𝑘 ∙ 𝑤𝑤𝑖𝑖𝑖𝑖𝑖𝑖 ∙ 𝑤𝑤𝑡𝑡ℎ(A-2.6)

where 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (𝑡𝑡) is the ecological activity of 131I in the thyroid due to ingestion (kBq) at day twith initial condition of 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (0) = 0; 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (𝑡𝑡 − 1) is the ecological activity of 131I in the
thyroid at day t-1 (kBq); Δ𝑡𝑡 = 1 d is the calculation step; 𝜆𝜆𝑡𝑡ℎ,𝑘𝑘 = ln(2)⁄𝑇𝑇𝑏𝑏,𝑘𝑘 is the rate of
biological elimination of iodine from the thyroid for a person of age k (d-1); 𝑇𝑇𝑏𝑏,𝑘𝑘 is the biologicalhalf-time of iodine removal from the thyroid for a person of age k [ICRP, 1993] (d); 𝜆𝜆𝑟𝑟,𝐼𝐼−131 =0.0862/d is the radioactive decay rate of 131I; 𝐷𝐷𝐷𝐷 𝐼𝐼−131 (𝑡𝑡) is the concentration of 131I in tap waterat the location of residence at day t (kBq/L); 𝑉𝑉𝐷𝐷𝐷𝐷,𝑘𝑘 is the daily consumption of tap water for
person of age k (L/d); 𝑤𝑤𝑖𝑖𝑖𝑖𝑖𝑖 = 1.0 is the fraction of ingested iodine transferred to blood [ICRP,
1993] (unitless).
69.
The total ecological activity of 131I in the thyroid was calculated as the sum of ecologicalamounts from inhalation and ingestion:
𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 (𝑡𝑡) = 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ (𝑡𝑡) + 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 (𝑡𝑡)(A-2.7)

22

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Table A-2.10. Age- and sex-dependent parameters of the dosimetry model
Age(years)M

Hours per day indoors

Breathing rate
(m3/d)

Drinking water consumption
(L/d)

F

M

F

M

F

M

F

0

1.3

1.3

24

24

2.86

2.86

0.42

0.42

1

1.8

1.8

21.6

21.6

5.16

5.16

1.00

0.83

2

2.2

2.2

21.6

21.6

6.05

6.05

1.04

0.86

3

2.6

2.6

21.6

21.6

6.94

6.94

1.07

0.89

4

3.0

3.0

21.6

21.6

7.83

7.83

1.11

0.92

5

3.4

3.4

21.6

21.6

8.72

8.72

1.15

0.95

6

4.3

4.3

21.6

21.6

10.0

10.0

1.18

0.98

7

5.2

5.2

21.6

21.6

11.4

11.4

1.22

1.01

8

6.1

6.1

21.6

21.6

12.7

12.7

1.26

1.04

9

7.0

7.0

21.6

21.6

14.0

14.0

1.30

1.07

10

7.9

7.9

21.6

21.6

15.3

15.3

1.33

1.11

11

8.7

8.7

21.6

21.6

16.3

15.4

1.37

1.14

12

9.5

9.5

21.6

21.6

17.2

15.5

1.41

1.17

13

10.4

10.4

21.6

21.6

18.2

15.6

1.44

1.20

14

11.2

11.2

21.6

21.6

19.1

15.7

1.48

1.23

15

12.0

12.0

21.6

21.6

20.1

15.8

1.52

1.26

16

13.6

13.0

21.4

21.4

14.4

11.4

1.55

1.29

17

15.2

14.0

21.1

21.1

14.7

11.7

1.59

1.32

18

16.8

15.0

20.9

20.9

15.0

12.1

1.63

1.35

19

18.4

16.0

20.6

20.6

15.2

12.4

1.66

1.38

20

20.0

17.0

20.4

20.4

22.2

17.8

1.70

1.41

3.

70.

𝑚𝑚𝑡𝑡ℎ,𝑘𝑘 (g)Instrumental dose

The instrumental thyroid dose of subject k was calculated using the following equation:
𝐷𝐷𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 =𝑄𝑄𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 (𝑡𝑡𝑚𝑚 )∙ (𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ + 𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 ) = 𝑆𝑆𝑆𝑆 ∙ (𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖ℎ + 𝐷𝐷𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒,𝑖𝑖𝑖𝑖𝑖𝑖 )𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 (𝑡𝑡𝑚𝑚 )= 𝐷𝐷𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖,𝑖𝑖𝑖𝑖ℎ + 𝐷𝐷𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖,𝑖𝑖𝑖𝑖𝑖𝑖(A-2.8)where 𝑄𝑄𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 (𝑡𝑡𝑚𝑚 ) is the activity of 131I measured in the thyroid calculated using equation A-2.3(kBq); 𝑄𝑄𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 (𝑡𝑡𝑚𝑚 ) is the ecological activity of 131I in the thyroid at the time of measurement 𝑡𝑡𝑚𝑚
calculated using equation A-2.7 (kBq); and 𝑆𝑆𝑆𝑆 is a scaling factor (unitless).
4.

Model parameters(a)Biokinetic parameters

71.
The Committee estimated the amounts of 131I in measured thyroids and the related
absorbed doses for intakes by inhalation and ingestion using biokinetic models of ICRP [ICRP,ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

23

1989; ICRP, 1993; ICRP, 1995], albeit corrected for Japan-specific iodine uptake by thyroid (seesection IV).
(b)

Thyroid mass

72.
The thyroid mass is one of the most important parameters in the estimation of thyroid
doses and uncertainty in its value is the major contributor to the overall uncertainty whenestimating thyroid doses [Drozdovitch et al., 2015]. The Committee used age- and sex-specificvalues of the thyroid mass from ICRP Publication 89 [ICRP, 2002] to calculate thyroid doses(see table A-2.10).
(c)Number of hours spent indoors

73.
The number of hours spent indoors by different age groups in the population were thosespecified in attachment A-4 in the estimation on external doses from deposited radionuclides(see table A-2.10).
(d)Breathing rate

74.
Breathing rates were taken from ICRP [ICRP, 2002] and are summarized in table A-2.10
for various ages.
(e)Drinking water consumption

75.
Daily consumption of tap water was taken to be 1.0 L for 1-year-old infant and 1.7 L for
adults [Hirakawa et al., 2017] and 1.5 L for 10-year-old children. Consumption by females was
adjusted by a factor of 0.83 derived from an analysis of water consumption in Japan [IAEA,
1998]. Daily consumption for 3-month-old infants was taken to be 0.42 L based on assumed
breastfeeding, a transfer coefficient of 131I of 0.37 (d/L) from intake to breast milk [Simon et al.,2002], and consumption of breast milk by an infant of 0.8 L/d. It should be noted, that there isvariability in daily consumption of drinking water reported in literature from 0.71 L to 1.3 L fora 1-year-old infant, from 1.55 L to 2.2 L for a 10-year-old child and from 1.55 L to 2.3 L for
adults [Miyatake et al., 2020; Murakami and Oki, 2014].
(f)

Iodine-131 concentrations in air at locations and times where those measured were
exposed76.
Daily time-integrated concentrations of 131I in air were obtained using the modelling
approach described in section V. Population-weighted arithmetic mean values of the daily timeintegrated concentrations were estimated for permanent residents of one or other municipality
where thyroid measurements were made. For evacuees, account was taken of their whereabouts
before, during and after evacuation in estimating the population-weighted daily integrated air
concentrations. For some municipalities different evacuation routes were followed by different
groups resulting in them being exposed to different concentrations of 131I (see section VII.C andtable A9 in appendix A). In such cases (e.g., Iitate Village) the daily population-weighted mean
concentrations were estimated taking account of the fraction of the evacuated population
evacuating by the different routes.

24

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

(g)

Iodine-131 concentrations in tap water

77.
Iodine-131 concentrations in tap water for each of the municipalities where thyroids were
measured were estimated by [Miyatake et al., 2020] and derived from [Kim et al., 2020; Kinase
et al., 2014; Murakami and Oki, 2014]. Figure A-2.V shows the variation with time of measured
131
I activity concentration in tap water in locations with direct thyroid measurements (restrictions
are not shown).
Figure A-2.V. Variation with time of measured 131I concentration in tap water in locations withdirect thyroid measurements (restriction in water consumption are not shown)

VIII. VALIDATION OF THE MODELS AND APPROACHES USED BY
THE COMMITTEE FOR ESTIMATING DOSES FROM THE INTAKE
OF 131I BY INHALATION AND INGESTION
78.
Thyroid doses, estimated by the Committee using models and approaches that it judged
appropriate for these purposes, have been compared with those derived from direct
measurements of thyroids. The modelled doses were estimated following the approaches set out
in sections IV, V and VI of this attachment – but only for the intake of 131I as shorter-lived
isotopes of iodine would no longer have been present in the thyroids of those measured at thetime/s of measurement. The modelled ingestion doses were based on analyses undertaken by[Miyatake et al., 2020; Murakami and Oki, 2014] and are summarized in table A-2.11.
Table A-2.11. Indicative estimates of thyroid doses from ingestion based on references[Miyatake et al., 2020; Murakami and Oki, 2014]
Absorbed dose to thyroid due to 131I ingestion (mGy)
Location
Adults10-year old

1-year old

Permanent residents of Fukushima Prefecture, both food anddrinking water

0.42

0.94

1.1

Evacuees from Iitate Village (mean/median), drinking water

1.1/1.0

2.3/2.1

3.6/3.3

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

25

79.
Comparison of the modelled doses estimated by the Committee and those derived fromindividual thyroid measurements was made in terms of the ratio “modelled dose” to“instrumental dose”, unitless, in two ways: (a) comparison of the median modelled dose (frominhalation and ingestion) with median instrumental dose derived from direct thyroid
measurements, for each age and municipality where measurements were made; and(b) comparison of the median modelled dose (from inhalation and ingestion) with individual
instrumental dose derived from direct thyroid measurements on 1,103 persons. This comparison
does not include 40 persons from Minamisoma City (scenario 1) and Namie Town (scenario 1)
who were evacuated shortly after the accident.
A.

Issues with scaling factors

80.
The values of the scaling factors for 1,146 individuals with direct thyroid measurements
are shown in figure A-2.VI as a function of the age of those measured. The value of 𝑆𝑆𝑆𝑆 varies
with decreasing age and is most apparent for ages less than about 7 years. Such age dependence
was not observed among 11,732 subjects of the Belarusian-American cohort [Drozdovitch et al.,2013] and 13,204 subjects of the Ukrainian-American cohort [Masiuk, 2019].
Figure A-2.VI. Scaling factor for 1,146 measured individuals versus age. Yellow diamonds show
median of scaling factors for given age

81.
The possible reasons for this trend or bias include: (a) particularities in the behaviour andlifestyle for children that were not considered in the modelled dose estimates; (b) different
geometry of the measurements (e.g., distance between the neck and the probe or/and part of the
body where measurements of background were made) applied for younger and older children
during the measurements; (c) calibration factors for the thyroid detectors used to measured
individuals; (d) higher iodine uptake by the thyroids of younger children owing to dietary habits
more akin to those in the west. To eliminate bias related to the age of measured individuals,
values of the scaling factor were analysed for each location of measurement and values of thescaling factor for young children were adjusted to those for age of 10 years and older. Scaling
factors for Minamisoma City and Namie Town were not adjusted, as bias related to age was notobserved for these locations.

26

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

B.

Thyroid doses derived from thyroid measurements

82.
The general characteristics of the doses derived from measurements of the thyroids of
1,080 individuals are shown in table A-2.12 for three municipalities. Those measured in Iitate
Village received the highest doses (arithmetic mean of 6.0 mGy), followed by Iwaki City
(4.1 mGy) and Kawamata Town (4.0 mGy). The maximum dose was 50 mGy for an individual
measured in Iitate Village.
Table A-2.12. General characteristics of thyroid doses (mGy) derived from thyroid
measurements
Parameter

Iitate Village

Iwaki City

Kawamata Town

Total

Number of individuals

299

134

647

1 080

Arithmetic mean

6.0

4.1

4.0

4.6

Median

4.9

3.0

3.3

3.5

Range

1.8–50

1.0–26

1.2–23

1.0–5083.
The distribution of thyroid doses derived from measurements of the thyroid are shown intable A-2.13 for each municipality where measurements were made; the overall distribution isshown in figure A-2.VII. For 645 individuals of 1,080 measured (59.7%), the thyroid doses were
estimated to be in the range 2.0–4.99 mGy. Fifty-seven individuals (5.3% of the total) were
estimated to have received thyroid doses of 10 mGy or more.
Table A-2.13. Distribution of 1,080 individuals with direct thyroid measurements by location of
measurements and range of doseInterval of thyroid
dose (mGy)

Iitate Village

Iwaki City

Kawamata Town

Total

N

%

N

%

N

%

N

%

1.0–1.99

10

3.4

44

32.8

47

7.3

101

9.4

2.0–4.99

143

47.8

55

41.1.

447

69.1

645

59.7

5.0–9.99

110

36.8

28

20.9

139

21.4

277

25.6

≥10.0

36

12.0

7

5.2

14

2.2

57

5.3

Entire study

299

100.0

134

100.0

647

100.0

1 080

100.0

<1.0

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

27

Figure A-2.VII. Distribution of thyroid doses, derived from direct thyroid measurements, of
1,080 individuals in a few municipalities of Fukushima PrefectureC.

Comparison of thyroid doses derived from measurements withestimates published by others

84.
The Committee has compared its estimates of thyroid doses derived from measurementsof thyroids with those of Kim et al. [Kim et al., 2020]. Kim et al. considered two scenarios of131
I intake:− Scenario 1: single intake via inhalation on 15 March 2011; and− Scenario 2: repeated intake via ingestion at a uniform rate from 16 March 2011 to the
day before measurements.
85.
The two estimates are compared in table A-2.14 for Iitate Village, Iwaki City and
Kawamata Town. Comparisons, however, can only be made for some of the quantities of therespective distributions of dose owing to the different treatment of measurements where themeasured dose rate was equal to or less than the background. The Committee, in its assessment,
replaced such measured dose rates (for 598 (55%) of the 1,080 measured individuals) by thelower limit, while Kim et al. [Kim et al., 2020] assumed that the activity of 131I in the thyroid
was zero, as was the corresponding dose. Meaningful comparisons can, however, be made of themedian, upper quartile and maximum doses estimated; those estimated by the Committee can beseen in table A-2.14 to be in reasonable agreement with those of Kim et al. [Kim et al., 2020].
Thyroid doses estimated by the Committee are, in general, close to those estimated by Kim et al.
[Kim et al., 2020] for Scenario 1 of inhalation 131I intake. IAEA also analysed the same group of
1,080 measured individuals and concluded that predominant intake of 131I to the children was
due to inhalation rather than ingestion [IAEA, 2015].

28

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

86.
Kim et al. [Kim et al., 2020] also indicated that 73 individuals from among thosemeasured were from municipalities other than where the measurements were made, specifically,
from Minamisoma City and Fukushima City and two persons from Ibaraki Prefecture. These
individuals were not identified in the information made available to the Committee and are a
confounding factor.
87.
A comparison is also made in table A-2.15 between the doses estimated by the Committee
and those of Kim et al. [Kim et al., 2020] for measurements of the thyroids of residents of
Minamisoma City as reported by Tokonami et al. [Tokonami et al., 2012]. Althoughmeasurements were made in different groups of people of different ages, broad agreement isobserved between the two estimates for the median, upper quartile and maximum of the thyroid
dose distributions.

Table A-2.14. Comparison of thyroid doses (mGy) estimated by the Committee from direct measurements of the thyroid and those of Kim et al.
[Kim et al., 2020] for Iitate Village, Iwaki City and Kawamata Town
Iitate Village
Parameter

Iwaki City

[Kim et al., 2020]

Kawamata Town

[Kim et al., 2020]

This study

This study
Scenario 2
291

Scenario 1
134

Scenario 2
123

Scenario 1
647

Scenario 2

Number of persons

299

593

Minimum (mGy)

1.8

0.0

0.0

1.0

0.0

0.0

1.2

0.0

0.0

Lower quartile (mGy)

2.9

0.0

0.0

1.6

0.0

0.0

2.5

0.0

0.0

Median (mGy)

4.9

3.7

1.6

3.0

2.8

1.5

3.3

0.0

0.0

Upper quartile (mGy)

7.7

7.5

3.3

5.0

8.8

4.5

3.7

3.7

1.6

Maximum (mGy)

50

61

20

26

48

25

23

31

13

Interquartile range (mGy)

4.8

7.5

3.3

3.4

8.8

4.5

1.2

3.7

1.6

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Scenario 1[Kim et al., 2020]
This study

29

30

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Table A-2.15. Comparison of the thyroid doses (mGy) estimated by the Committee from direct
measurements of the thyroid and those of Kim et al. [Kim et al., 2020] for Minamisoma City
Minamisoma City
Parameter[Kim et al., 2020]
This study
Scenario 1

Scenario 2

Number of persons

45

Minimum (mGy)

0.11

0.0

0.0

Lower quartile (mGy)

1.0

0.0

0.0

Median (mGy)

1.9

2.8

1.3

Upper quartile (mGy)

4.7

7.5

3.3

Maximum (mGy)

27

26

11

Interquartile range (mGy)

3.7

7.5

3.3

1.

31

Variability of individual thyroid doses among those measured

88.
The variability of thyroid doses among those measured is shown in figure A-2.VIII where
normal probability plots (logarithm of values) are presented for different age groups.
Distributions of individual thyroid dose for age groups of 1-year-old infants and 10-year-old
children were found to be log-normal and the geometric standard deviation (GSD) characterizes
the uncertainty of the doses. Parameters of the distributions of individual thyroid doses fordifferent age groups are given in table A-2.16. Judgements on the form of the distribution of
adult doses are less definitive probably because of the relatively small number of adults
measured.
Figure A-2.VIII. Normal probability plots of thyroid doses (logarithm of values) of individuals ofdifferent ages whose thyroids were measured in one or other municipality of Fukushima
PrefectureANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

31

Table A-2.16. Parameters of the distributions of individual thyroid doses derived from thyroid
measurements

Population group

Parameters of thyroid doses distribution(relative units)

Number of
persons
5%

50%

Mean

95%

GSD

1 year (preschool children)

425

0.50

0.84

1.00

2.10

1.8

10 years (school children)

662

0.43

0.75

1.00

2.51

2.1

Adults (>16 years)

56

0.03

0.34

1.00

4.51

4.3

All

1 143

0.35

0.75

1.00

2.58

2.1

2.

Uncertainties in thyroid doses derived from measurements

89.
The uncertainty of individual thyroid doses is characterized by the GSD for a log-normal
distribution of individual stochastic doses calculated for each person using Monte Carlosimulations. The Committee has not made a quantitative assessment of the uncertainties in thedoses it has derived from thyroid measurements; rather, it has relied on extensive assessments ofuncertainties in thyroid doses derived from thyroid measurements of those exposed to Chernobyl
fallout where GSD values ranged from about 1.5 to 1.8 [Drozdovitch et al., 2015; Likhtarov etal., 2014]. Based on the Chernobyl experience, the Committee has made a subjective judgementthat a GSD of about 2 would be appropriate for the distribution of individual thyroid dose in themunicipalities of Fukushima Prefecture where thyroids were measured.
D.

Comparison of modelled and measured thyroid doses from intakesof 131I90.
A comparison of the modelled doses estimated by the Committee and those derived frommeasurements is given in table A-2.17. Median doses, together with uncertainties in their values(5% and 95% confidence intervals), are presented for each of the municipalities where thyroids
were measured. The confidence intervals on the modelled doses were estimated following theapproach set out in attachment A-12; those on the measured doses were based on expert
judgement (see section VII.B). The modelled doses are, on average, in broad agreement withthose derived from direct thyroid measurements. The weighted average ratios over all ages ofthe modelled and measured median doses range from 0.46–0.91 for the municipalities where
measurements were made.
91.
The distribution of the ratio of modelled and measured median thyroid doses is shown infigure A-2.IX. The ratio varies over quite a wide range up to values of about 3.7. The mean andmedian values of the ratio are 0.64 and 0.6, respectively.
92.
The broad agreement between the modelled and measured doses, albeit in a small numberof municipalities where thyroid measurements were made, supports the use of the models andapproaches adopted by the Committee for estimating thyroid doses to the Japanese population.

Adults (16 years+)
Locality

Ratio (modelledto-measured),
relative units

Model
(mGy)

Thyroid
measurements(mGy)

Ratio (modelledto-measured),
relative unitscThyroid
measurements(mGy)

Ratio (modelledto-measured),
relative units

1.42[0.53–9.8]b

2.34[1.1–14]

3.57 (220)c[1.1–11]

0.66

2.75
[1.3–16]

7.11 (79)[2.3–22]

0.39

Iwaki City

1.19
[0.53–7.1]

2.21[1.1–12]1.75 (79)[0.56–5.5]

1.26

2.64
[1.3–15]

4.55 (55)[1.5–14]

0.58

Kawamata Village

0.95[0.49–9.1]

1.81[1.0–15]

2.56 (361)[0.82–8.0]

0.71

2.12
[1.2–18]

4.50 (286)[1.4–14]0.47

Minamisoma City d

5.81[1.1–41]

6.53 (15)[2.1–20]

0.89

9.9[2.1–69]

12[2.5–84]

10.2 (1)[3.3–32]

1.17

Namie Town

21.5
[2.6–281]

20.7 (6)[6.6–65]

1.04

36.0
[4.6–467]

41.3

Tamura City

0.50
[0.43–3.0]

1.22 (1)[0.39–3.8)]

0.41

1.07
[0.96–5.3]

1.24

0.91

Limited to 1,103 of the 1,146 thyroid measurements, as meaningful comparisons could not be made for the others.
Fifth and 95th percentiles given in square brackets.
Number of measured individuals given in parenthesis.
dExcluding those evacuated soon after the accident.
eWeighted by number of measured individuals.
b

Model
(mGy)

0.76

0.47

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Thyroid
measurements(mGy)

1-year old (≤5 years)

10-year old (6–15 years)

Iitate Village

Mean ratio e
a

Model
(mGy)

32

Table A-2.17. Comparisona of modelled and measured median doses (and 5th and 95th percentiles) to the thyroids of 1,103 individuals whose
thyroids were measured in particular municipalities of Fukushima PrefectureANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

Figure A-2.IX. Distribution of the ratios of modelled to measured thyroid doses, unitless

33

ANNEX B, ATTACHMENT A-2: THE ESTIMATION OF THYROID DOSES RESULTING FROM THE ACCIDENT …

35

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