保健医療科学

2018 Vol.67 No.1 p.11－20

Topics: Lessons learned on public health from the Fukushima Daiichi Nuclear Power Plant accident＜ Review ＞
External and internal dose assessments of Fukushimaresidents after the 2011 nuclear disaster
Osamu Kurihara
National Institute of Radiological Sciences of National Institutes for Quantum and Radiological Science and Technology

Abstract
Much effort has been made by Japanese experts to assess the dose to residents of Fukushima Prefecturein the aftermath of the 2011 nuclear disaster. Residents living near the Fukushima Daiichi Nuclear Power
Plant (FDNPP) were ordered to evacuate promptly after the accident to minimize radiation exposure.
Many papers performing individual dose measurement and estimation of these residents have alreadybeen published. This paper provides a brief overview of these publications by dividing the evaluation into
the early-phase (< 1 year) and the late-phase (≥ 1 year) studies, and compiling the lessons learnt fromthe 2011 nuclear disaster. One common view of the studies by the Japanese experts is that the levels of
exposure are generally low. Aside from the internal thyroid dose from short-lived radionuclides (mainly 131I)
at the early phase, both the external and internal doses attributable to the nuclear disaster are comparable
or less than those from natural radiations. A number of individual dose measurements at the late phasehave provided useful information for understanding exposure situations in everyday life for people living in
the affected area. One key remaining issue for the dose assessment is to evaluate the related uncertainty, inparticular for the internal thyroid dose received at the early phase. Thus, there is a role for further studies
to improve the certainty of dose estimations.
keywords: Fukushima Daiichi Nuclear Power Plant, dose assessment, external dose, internal dose, nuclear
accident, residents(accepted for publication, 8th December 2017)

I．IntroductionMore than 7 years have passed since the natural
disaster affecting the Fukushima Daiichi Nuclear Power
Plant (FDNPP) run by Tokyo Electric Power Company(TEPCO) in March, 2011. The resulting accident caused
contamination by radionuclides across a wide area of
East Japan [1]. A large number of residents living in themunicipalities near the FDNPP were ordered to evacuate
promptly after the accident in order to prevent radiation
exposure [2]. The total amounts of iodine-131 (131I) andcesium-137 (137Cs) released to the atmosphere from March
12 to May 1, 2011 were estimated to be 151 PBq and14.5 PBq, respectively [3], which roughly correspond to
one-tenth and one-fifth of the amounts in the Chernobyl
accident [4]. Much effort has been made to understandthe extent of radiation exposure of residents in Fukushima
Prefecture. One common view of the various publications
by Japanese experts is that both the external and internal
doses of the residents due to the accident were generally
low. Therefore, the future radiation-induced health risks are
expected to be undetectable. However, there still remain
problems in the dose assessment, such as the related
uncertainty, in particular for the early internal dose of 131I,
and particularly the thyroid exposure experienced by smallchildren. This paper provides a brief overview of the major

Corresponding author: Osamu Kurihara
4-9-1 Anagawa, Inage-ku, Chiba-shi, Chiba 263-8555, Japan.
Tel: +81-43-206-3025 (outside of Japan), or 043-206-3025 (in Japan)
E-mail: kurihara.osamu@qst.go.jp

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Osamu Kurihara
dose assessment results of the residents by dividing into
studies into early- (< 1 year after the accident) and late(≥ 1 year) phase studies, and identifies important lessons
learnt from the experiences in the FDNPP accident.

II．External dose assessment
1. Early phase
The residents living in the municipalities near the
FDNPP were ordered to evacuate their hometowns
shortly after the accident from their hometown [2]. Some
residents were forced to evacuate many times because of
repeated expansion of the restricted zone by the Japanese
Government repeatedly. The first exploratory committee ofFukushima Health Management Survey (FHMS) was heldat the end of May, 2011 and an external dose assessment
for all residents in Fukushima Prefecture (~2 millions) was
proposed as a part of FHMS (Basic Survey) [5]. Fukushima
Prefecture commissioned Fukushima Medical University(FMU) as the organization responsible for the FHMS. For
this survey, it was decided that an external dose assessment
be performed based on the personal behavioral data (i.e.,
the whereabouts of the person after the accident) derived
from self-administrative questionnaires. To facilitate this,the National Institute of Radiological Sciences (NIRS,
currently, reorganized as one of the directorates of National
Institutes for Quantum and Radiological Science andTechnology, QST) developed an external dose estimation
system and computed external doses of hypotheticalpersons with 18 evacuation scenarios to grasp the levelsof external doses to real persons in advance of the datagathering [6]. This system utilized both digitized personal
behavioral data and the chronological data of ambient dose
rate maps in Fukushima Prefecture. The latter dataset was
created based on a simulation by the System for Predictionof Environmental Emergency Dose Information (SPEEDI)
for the period from March 12 to 14 and the measurement
data by Ministry of Education, Culture, Sports, Science andTechnology (MEXT) for the period from March 15 and later.
The system considered a structural shielding factor (=indoor/outdoor ambient dose rate) depending on the typeof building, and a body size correction factor with age. Notethat the system calculated the effective dose from external
irradiation for the first four months only after the accident.
As a result, the maximum dose was 19 mSv for the delayed
evacuation scenario from one place in Iitate village which
the Japanese Government designated as the deliberate
evacuation area for relocation in April 2011. The doses forthe prompt evacuation scenarios from the 20 km radius of
the FDNPP were relatively low.
Using this system, the external dose estimation of the12

residents has been continued to the present. The numberof the residents whose external doses were estimatedreached 552,298 as of 30 June 2017. As the intermediate
result, it was reported that the individual external doses forthe first 4 months were below 3 mSv for 99.4% of 421,394
residents (excluding radiation workers). The arithmetic
mean and maximum of the doses of the residents fromthe Soso region covering the municipalities within the
restricted zone (within the 20 km radius of the FDNPP)
were 0.8 mSv and 25 mSv, respectively [7]. Regarding themean dose, the doses of the Kenpoku and Kenchuo regions
where no evacuation orders were issued were higher thanthat for the Soso region. This suggested that the prompt
evacuation may have significantly reduced exposure dosesof the residents living near the FDNPP.
Several municipalities in Fukushima Prefecture initiatedexternal dose measurements of the residents using
passive-type personal dosimeters [8]. According to theresults of Fukushima city, the individual external dosefrom September 1 to November 30, 2011 (3 month) was
less than 1 for 99.7% of the 36,767 examined subjects
including infants, elementary and junior school students andpregnant women. The first-year average dose estimates ofFukushima city, Date city, Ninonmatsu city, Tamura city andKoriyama city were 2.1 mSv, 1.9-3.3 mSv, 2.4-2.5 mSv, 1.21.4 mSv and 1.7 mSv, respectively, by adding the resultsof the Basic Survey [9]. These estimates are smaller thanthose from the United Nations Scientific Committee on the
Effects of Atomic Radiation (UNSCEAR) 2013 report [10].
2. Late phase
In April 2012, the Japanese Government reorganized
the contaminated areas in the eastern part of Fukushima
Prefecture in accordance with the levels of the projectedannual external dose (excluding the dose from naturalradiation) [11]. The newly designated areas werecategorized into the followings: (1) difficult-to-return areas(> 50 mSv), (2) restricted habitation areas (20-50 mSv) and(3) evacuation-directive-lift prepared areas (< 20 mSv).
The projected annual external dose was calculated from theairborne survey in conjunction with a simple assumption,
namely 16 h for the time spent indoors and 8 h for thetime spent outdoors. A structural shielding factor (0.4)
was applied to the time spent indoors. For example, theprojected annual external dose of 20 mSv corresponds to-1
the ambient dose rate outdoors of 3.8μ Sv h excluding thecontribution from natural radiation.
However, a considerable discrepancy is often foundbetween the projected dose and the individual dose directly
measured with personal dosimeters (PDs). To clarify thisgap, many studies have been performed by recruiting

J. Natl. Inst. Public Health, 67 (1) : 2018

External and internal dose assessments of Fukushima residents after the 2011 nuclear disastervolunteers who wore PDs and recorded their time spentat each place in daily life [12-17]. As a result, it was foundthat the main cause for the discrepancy lay in the factthat the time spent outdoors was much shorter than 8 h
for most of the volunteers. The measured individual dose
was often smaller by several times the projected dose.
Other studies focused on the structural shielding factor of
inhabitant places [18] and the time variation of the dose
rate in daily life using electric PDs (e.g., D-shuttle) [12,13].
The estimated annual external doses in the late phase weregenerally lower than 1 m Sv y-1 in the non-evacuation areas[19,20] and were lower than the projected annual external
dose in the other areas [21,22].

III．Internal dose assessment
1. Early phase
Regarding internal exposure, the most concerning
radionuclide in the early phase is 131I with a physical half-lifeof about 8 days. Based on Chernobyl studies, radioiodine
contributes a significantly higher dose to the thyroid than
to the whole-body (effective dose) due to its biokinetic
behavior, which is of great concern in particular for smallchildren [23]. The Japanese Government regulated the
distribution and consumption of food and drink thatexceeded provisional regulation values for the radioactivity
concentration shortly after the accident [24]. In addition,a collapse in the food supply chain due to damage to
distribution facilities, lack of transportation vehicles orelectricity, and the closure of retail stores should havesignificantly reduced consumption of contaminated foodstuff
by people even before the implementation of restriction
orders [25]. However, there were still possible pathways forinternal exposure, such as inhalation of radioactive plumes
and ingestion of water very early after the accident, whichhave not been fully investigated.
The Nuclear Emergency Response Local Headquarters of
the Japanese Government conducted screening campaigns
for thyroid exposure of children (aged ≤ 15 y) at Kawamata
town, Iwaki city and Iitate village at the end of March, 2011[26]. The subjects totaled 1,080. The results showed that no
subjects exceeded the screening level corresponding to 100
mSv for hypothetical 1-y-old children with chronic intake
via inhalation of 131I from March 12 to 23 (12 days). Reviseddose estimations of the screening campaigns have been
published, demonstrating that the 90th percentile values of
the thyroid equivalent dose for Kawamata town, Iwaki cityand Iitate village were 7.3, 15.9 and 14.7 mSv, respectively[27]. Regarding the other direct human measurements to
identify 131I, Tokonami S, et al. have reported the results of
their measurements of residents and evacuees from Namie

town and Minamisoma city during the period from April
12 to 16 [28]. Significant 131I radioactivity in the thyroid
was found in 46 out of 62 subjects and the maximum
thyroid doses of children and adults were 23 mSv and 33
mSv, respectively. Matsuda N, et al. have also reported
their results from evacuees and responders who visited to
Fukushima Prefecture for a short period of time [29]. The
number of the subjects totaled 173. The measurements
were performed within one month after the accident using
a whole-body counter (WBC). 131I, cesium-134 (134Cs) and137
Cs were significantly detected from more than 30% of theexamined subjects. The maximum thyroid equivalent dosewas 20 mSv. Meanwhile, Kamada N, et al. estimated thyroid
doses of 15 residents of Kawamata town and Iitate village
based on the urine samples taken on May 5 and from May
29 to June 6, 2011 [30]. In 5 of the 15 subjects tested, 131I
was detected in the urine samples; the thyroid equivalentdoses were 27–66 mSv.
Afterwards, Fukushima Prefecture decided to perform
further individual monitoring using WBC units to respondto a growing concern about internal exposure among theresidents. This task was initially commissioned to NIRS
and Japan Atomic Energy Agency (JAEA) at the beginning.
NIRS performed WBC measurements of 174 subjects
mainly from Namie town, Kawamata town and Iitate village
during the period from June 27 and July 28, 2011 [31].
At this time, only 134Cs and 137Cs were the only targetedradionuclides because 131I had completely decayed out by
this time. As a result, the number of the subjects withsignificant detection of both 134Cs and 137Cs were relatively
small: 28.8% for adults and 4.1% for children. The 90th
percentile and maximum committed effective dose (CED)
for the adults from 134Cs and 137Cs were 0.1 mSv and 0.63
mSv, respectively. JAEA reported the results of the firstyear WBC measurements of the 9,927 residents fromthe areas where evacuation orders were issued [32]. The
major findings are as follows: (1) 22 subjects (including
21 children aged ≤ 12 y) exceeded 1 mSv (the maximum
CED: 3 mSv); (2) the (extrapolated) median CED values of
the two age groups of 13–17 y and > 17 y were 0.02 mSv
and 0.025 mSv, respectively; (3) the 95th percentile CED
value of all the subjects was ~0.1 mSv; (4) the CEDs of thechildren (< 8 y) from whom Cs was significantly detected
were much higher than those of their parents or elderlyfamily members. Note that a common intake scenario,
namely acute inhalation on March 12, 2011, was applied to
the WBC measurements by the two institutes. This mightlead to an overestimations of the internal dose of residents
because of possible incidents of intake at a later time period
than the assumed intake day.
WBC measurements were also started by several

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Osamu Kurihara
hospitals where WBCs were independently installed at an
early phase. Tsubokura M, et al. measured 9,498 residents(1,432 children and 8,066 adults) of Minamisoma city forthe period between September 26, 2011 and March 31,
2012 [33]. A detectable amount of Cs was found in 3,268 of
the subjects (235 children and 3501 adults), with only one
person exceeding a dose of 1 mSv (1.07 mSv). Hayano RS,
et al. also reported the results of the WBC measurementsof 32,811 subjects at Hirata Central Hospital for the period
from October 17, 2011 to November 30, 2012 [34]. The
Cs detection rate was lower in children than in adults, anddecreased with time. High Cs body contents were detected
in a small part of the subjects who evidently consumed
contaminated foodstuff, such as wild mushroom. The
maximum CED was found to be 1.06 mSv.
Other than the direct human measurements, themonitoring results of radioactivity in food and water wereused to estimate the ingestion dose [35-38]. It was pointed
out that the ingestion dose evaluated by World HealthOrganization (WHO) and UNSCEAR was overestimatedbecause of conservative assumptions, such as continuing
consumption of contaminated items for a certain periodof time [10,39]. By contrast, Murakami and Oki took into
account the effect of countermeasures implemented after
the accident in their estimation of the ingestion doses ofcitizens of Fukushima city, Tokyo and Osaka [40]. The
average thyroid equivalent doses of citizens (adults) of
Fukushima city, Tokyo and Osaka from 131I were 2.7 mSv(Case 2), 0.37 mSv, 0.016 mSv, respectively. The average
effective doses from 134Cs and 137Cs of the same groups fromwere 0.12 mSv (Case 2), 6.1μSv, 1.9μSv, respectively.
Several studies by Japanese experts also conducted foodduplicate surveys at an early phase, demonstrating that theingestion dose from 134Cs and 137Cs was much lower than
1 mSv per year [41,42]. As the most recent publication
related to ingestion from tap water, Kawai M, et al. reported
the estimated ingestion dose from 131I at the early phasewith a consideration of realistic intake scenarios based on
their survey [43]. The maximum thyroid equivalent dosesof 1-year-olds, 10-year-olds and adults of the evacuation
areas were estimated as 22, 11 and 4.7 mSv, respectively.
Those of the same groups from the non-evacuation areas
were 9.5, 4.7 and 2.0 mSv, respectively. Another recent
publication by Ohba T, et al. focused on the body surface
contamination levels of evacuees from the areas near the
FDNPP, demonstrating a difference in the levels dependingon the route of evacuation [44]. This study also evaluatedthe contribution of the short-lived radionuclides other than131
I (132Te/132I, 133I and 135I). These radionuclides may givea significant internal dose if the intake event is limited toMarch 12, 2011 [45].

142. Late phase
The number of WBCs available for measurements of theresidents has increased in the past years. More than 50
WBCs (including mobile units) currently exist in Fukushima
Prefecture [46]. Fukushima Prefecture has continued theWBC measurements of the residents (including voluntaryevacuees to places outside Fukushima), and the numberof the subjects has reached 327,434 as of October, 2017[47]. The number of persons whose CED is greater than orequal to 1 mSv is 26, which has increases by only 4 persons
compared to the results in 2012 (see above). This result
suggests that a risk of internal exposure has been very
limited in the late phase. Several other studies have also
demonstrated an extremely low detection rate in the otherWBC measurements thanks to detailed and comprehensive
food inspections [48-50]. Meanwhile, it has been found that
there are a small proportion of persons with significantly
high body contents of radiocesium [51]. This was identified
as being caused by ingestion of non-inspection food items
and tends to be seen in elderly persons [52].

IV．Discussion
The main objective of the dose assessment in radiation
accidents is to provide information for evaluating the degreeof radiation-induced health risk and/or judging the necessityof radiation protection measures. It is also recognizedthrough the experiences of the FDNPP that the informationfrom the dose assessment should be used not only fordecisions by authorities or experts, but also for supportof the residents through the related communications.
The importance of paying attention to social, ethical,
and physiological issues is emphasized in the recent EU
recommendations for preparedness and heath surveillanceof the populations affected by a radiation accident [53].
However, the discussion here is mainly focused on technicalissues in the external and internal dose assessments of theresidents.
1. External dose assessment
The internal dose estimation performed as apar t of FHMS has been completed for about onequarter of the target subjects (~ 2 million residents inFukushima Prefecture). The number of answerers forthe questionnaires about personal evacuation behaviors
has almost reached a plateau. An additional survey has
confirmed that the external doses of the one-quarter
subjects are representative of those of the entirety ofthe target subjects [54]. Further studies would be thus
desired on the tendency of the dose distributions for each
representative evacuation group that is extracted fromJ. Natl. Inst. Public Health, 67 (1) : 2018

External and internal dose assessments of Fukushima residents after the 2011 nuclear disaster
actual personal behaviors data and the uncertainty in thecurrent dose estimation, and so on.
One important issue in the late phase was the earlier
mentioned discrepancy between the projected dose andthe individual external dose directly measured with PDs.
The Japanese Government stressed the importance ofcontinuous monitoring for individual doses as accurately
as possible and stated that the decision to return homeshould be made on the measured individual external doses(e.g., reading of the PDs) rather than the estimations
based on the ambient dose rate [11]. In this context, NIRS
and JAEA investigated the relationship between the twodoses at several places in Fukushima Prefecture [55,56].
As a result, it was found that the readings of the PDs wornby adult males of average body size were about 0.7 times
as large as the ambient dose at the same places and thatthe two doses were well proportional to each other [57].
The ratio is somewhat increased for subjects with small
body sizes (e.g., children) because of the lesser shielding
effect by the body against radiation coming from the back.
Although this finding often gave the impression that thePDs underestimated individual external doses, Monte
Carlo simulations suggested that the readings of the PDs
would offer a good approximation of the effective dose of
the subject under an environment where radiocesium iswidely distributed in the ground [58,59]. This is important
knowledge for ensuring the validity of the current individual
external dose measurements in the affected areas.
Recent individual external dose measurements havebeen performed by utilizing the latest technologies(e.g, the combination of a D-shuttle and a GPS system)[12,13,60]. These devices provide an individual information
on when and where he or she faces the most exposure toradiations in daily life. Such information would be usefulfor considering a method to reduce exposure effectively
or as one of the risk communication tools to understandradiation sources encountered in everyday life together
with explanations by experts. The importance of this kindof support to the affected population is also emphasized in
the recommendations [53].
2. Internal dose assessment
The most important issue in the internal dose assessment
is the difficulty in estimating the early internal doses of the131
residents from short-lived radionuclides mainly I. Thisis because of the lack of direct human measurement data
related to 131I, which totals only ~1,300 data. Most of thesedata were obtained from a screening campaign based ona simplified measurement technique [26]. The number ofthe subsequent WBC measurements was relatively large;
however, these measurements could not detect 131I. Thus,

various methods have been proposed for estimating theearly internal dose, in particular, the thyroid dose due to thepotential intake of 131I and other short-lived radionuclides[27]. According to the dose estimations published up to thepresent, the upper levels of the CEDs from 134Cs and 137Cs
and the thyroid equivalent doses from 131I are ~0.1 mSv
and 20~30 mSv for the residents of Fukushima Prefecture,
respectively. The estimation of the thyroid equivalentdoses needs to be further improved, taking into account theintervention dose level to reduce the stochastic effect on
the thyroid, 50 mSv [61]. The representativeness of thosesubjects who underwent the screening campaign among the
populations in the areas of concern should also be examined.
One method of evaluating the thyroid equivalent doses
from the WBC measurements targeting radiocesium is todetermine the intake ratio of 131I to 137Cs (or 134Cs). Several
studies have derived this intake ratio from the direct humanmeasurements at the early phase [62-64]. The values ofthese studies were largely different from each other andtended to be smaller than the activity ratios of the two
radionuclides in environmental samples. These results
seem to be natural because of differences in the conditionsof each study and the relatively low thyroid iodine uptake(TIU) factor in the Japanese compared to that in the
biokinetic model for iodine [62,63]. However, this crucial
factor used for the dose reconstruction should be further
evaluated.
It is also important to recognize the uncertainty inthe internal dose estimation. The intake amount can becalculated based on a combination of parameters, including
breathing volume and amount of food and water intake
paired with time-series of the radioactivity in drinking
water, foodstuff and air. However, precise values of theseparameters are often difficult to obtain in the case of
emergency situations as a nuclear accident. Food and water
intake can be significantly different from that in normal
situations. Thus, detailed interviews of personal behaviors
for the persons of concern are necessary. The time ofevacuation and the occupation of the individual are also
important [65].
However, the uncertainty should be taken into accounteven in the internal dose estimation from the direct
human measurements. The assumptions made in theintake scenario (the time of intake and the route of intake)greatly influence the internal dose estimate. In the WBC
measurements by Fukushima Prefecture, two common
intake scenarios have been used: an acute intake scenario
by inhalation on March 12, 2011 (for subjects measured
between June 27, 2011 and January 31, 2012) and a chronic
intake scenario by ingestion from March 12, 2011 to one
day before the measurement day (for subjects measured

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Osamu Kurihara
from February 1, 2012 to the present) [32]. The acuteintake scenario was used to avoid underestimation of theinternal dose; however, it was found that this scenario
could not be accurately applied to younger age groups as
the measurements came too late. This was because of therapid decrease of whole-body retention rates of radiocesium(134Cs, 137Cs) for these groups over time. As a result, thesmall amount of the body content occasionally detected
was converted to an extremely large amount of intake.
Momose reported a large discrepancy in the CEDs between
the children with detection of radiocesium in their WBC
measurements and their parents; the CEDs of the children
were considerably higher than those of the parents [32].
However, this is unlikely to occur in real situations because
the intake amount should be larger in the adults than in
the children, whereas the internal dose coefficients (doseper unit intake: Sv Bq -1) of the adults and the children
are similar to each other. The detection in the WBC
measurements may be partly related to slight contaminationon the subject’s clothes brought back from houses in theaffected areas during temporal visits. To avoid the falsepositive detection, the subjects were asked to change into
contamination-free gowns before their WBC measurements.
From the viewpoint of the dose reconstruction, it isimportant to clarify how long the evidence of the early
intake remains in the WBC measurements.
At the late phase, the number of WBCs available has
been increasing. To the present, more than 50 WBCs exist
in Fukushima Prefecture alone [46]. A periodical check on
the accuracy of these WBCs has been performed by NIRS,
demonstrating that the WBC measurements in Fukushima
Prefecture are of sufficient quality [66]. As described earlier,the WBC measurements at the late phase have suggested
that the levels of internal exposure are minimal. However,
the experts have stressed that it is of great importanceto continue the WBC measurements of the residents inFukushima Prefecture.

V．Conclusion and Perspective
Much effort has been made to obtain external andinternal dose assessments of residents of Fukushima
Prefecture. One common view of the related publications
by Japanese experts is that the exposure dose related to the2011 nuclear disaster in Fukushima is minimal. It is thus
expected that radiation-induced health effects would beundetectable. This should be largely attributed to prompt
radiation protection measures for the residents. A numberof individual dose measurements at the late phase provide
not only information on the levels of exposure received ineveryday life, but also data useful for understanding the16

radiation. One remaining issue in the dose assessment is toevaluate the related uncertainty, in particular for the earlyinternal dose, mainly from 131I. Additionally, it is necessary
to use the lessons learnt from the 2011 nuclear disasterto establish a feasible and effective population monitoringprocedure in case of a future nuclear accident.

Acknowledgement
The author would like to thank Dr. Eunjoo Kim for careful
review of the manuscript.

Conflict of Interest
The author declares that there is no conflict of interests
regarding the publication of this article.

References[1] Saito K. Mapping and modeling for radionuclide
distribution on the ground due to the Fukushima
accident. Radiat Prot Dosimetry. 2014;160:283-287.
[2] The National Diet of Japan. The official report of
the Fukushima Nuclear Accident Independent
Investigation Commission Executive summary. 2012.
https://www.nirs.org/wp-content/uploads/fukushima/
naiic_report.pdf (accessed 2017-12-06)[3] Katata G, Chino M, Kobayashi T, Terada H, Ota M,
Nagai H, et al. Detailed source term estimation of
the atmospheric release for the Fukushima Daiichi
nuclear power station accident by coupling simulationsof atmospheric dispersion model with improved
deposition scheme and oceanic dispersion model.
Atoms Chem Phys. 2015;15:1029-1070.
[4] United Nations Scientific Committee on the Effectsof Atomic Radiation. Sources and effects of ionizing
radiation: UNSCEAR 2000 REPORT Vol. II. Annex J.
2000.
[5] Fukushima Prefecture. Exploratory Committee of
FHMS. http://www.pref.fukushima.lg.jp/site/portal/
kenkocyosa-kentoiinkai.html (accessed 2017-12-06) (inJapanese)[6] Akahane K, Yonai S, Fukuda S, Miyahara Y, Yasuda H,
Iwaoka K, et al. NIRS external dose estimation system
for Fukushima residents after the Fukushima Dai-ichi
NPP accident. Sci Rep. 2013;3:1670.
[7] Ishikawa T, Yasumura S, Ozasa K, Kobashi G, Yasuda H,
Miyazaki M, et al. The Fukushima Health Management
Survey: estimation of external doses to residents inFukushima Prefecture. Sci Rep. 2015;5:12712.
[8] Nagataki S, Takamura N, Kamiya K, Akashi M.

J. Natl. Inst. Public Health, 67 (1) : 2018

External and internal dose assessments of Fukushima residents after the 2011 nuclear disaster
Measurement of individual radiation doses in residents
living around the Fukushima nuclear power plant.
Radiat Res. 2013;180,439-447.
[9] Ishikawa T. Radiation doses and associated risk fromthe Fukushima Nuclear Accident: a review of recent
publications. Asia Pacific Journal of Public Health.
2017;29(2s):18S-28S.
[10] United Nation Scientific Committee on the Effect ofAtomic Radiation. UNSCEAR 2013 report volume
1 Scientific Annex A: Levels of effects of radiation
exposure due to the nuclear accident after the 2011
Great East-Japan Earthquake and tsunami. 2014.
[11] Nuclear Regulation Authority. http://www.nsr.go.jp/
data/000049323.pdf (accessed 2017-12-06) (inJapanese)[12] Naito W, Uesaka M, Yamada C, Ishii H. Evaluation ofdose from external irradiation for individuals using
areas affected by the Fukushima Daiichi nuclear power
plant accident. Radiat Prot Dosimetry. 2014;163(3):353361.
[13] Naito W, Uesaka M, Yamada C, Kurosawa T, Yasutaka
T, Ishii H. Relationship between individual external
doses, ambient dose rates, and individuals’ activitypatterns in affected areas in Fukushima following the
Fukushima Daiichi nuclear power plant accident. PLos
One. 2016;11(8):e0158879.
[14] Miyazaki M, Hayano R. Individual external dosemonitoring of all citizens of Date City by passive
dosimeter 5 to 51 months after the Fukushima NPP
accident (series): I. Comparison of individual dose andwith ambient dose rate monitored by aircraft surveys. J
Radiol Prot. 2017;37:1-12.
[15] Miyazaki M, Hayano R. Individual external dosemonitoring of all citizens of Date City by passive
dosimeter 5 to 51 months after the Fukushima
NPP accident (series): II. Prediction of lifetime
additional effective dose and evaluating the effect of
decontamination on individual dose. J. Radiol Prot
2017;37:623-634.
[16] Nomura S, Tsubokura M, Furutani T, Hayano RS, Kami
M, Kanazawa Y, Oikawa T. Dependence of radiationdose in the behavioral patterns among school children:a retrospective analysis 18 to 20 months following the2011 Fukushima nuclear incident in Japan. J Radiat
Res. 2016;57(1):1-8.
[17] Nomura S, Tsubokura M, Hayano R, Furutani T,
Yoneoka D, Kami M, et al. Comparison between direct
measurements and modeled estimates of externalradiation exposure among school children 18 to 30
month after the Fukushima nuclear accident in Japan.
Environ Sci Technol. 2015;49:1009-1016.

[18] Yoshida-Ohuchi H, Hosoda M, Kanagami T, Uegaki M,
Tashima H. Reduction factors for wooden houses due
to external γ-radiation based on in situ measurements
after the Fukushima nuclear accident. Sci Rep.
2014;4:7541.
[19] Tsubokura M, Kato S, Morita T, Nomura S, Kami
M, Sakakihara K, et al. Assessment of the annual
additional effective doses amongst Minamisomachildren during the second year after the Fukushima
Daiichi nuclear power plant disaster. PLos One.
2015;10(6):e0129114.
[20] Tsubokura M, Murakami M, Nomura S, Morita T,
Nishikawa Y, Leppold C, et al. Individual external
doses below level of 1 mSv per year five years after the2011 Fukushima nuclear accident among all children
in Soma city, Fukushima: a retrospective observational
study. PLos One. 2017;12(2):e0172305.
[21] Orita M, Hayashida N, Taira Y, Fukushima Y, Ide J,
Endo Y, et al. Measurement of individual doses ofradiation by personal dosimeter is important for the
return of residents from evacuation order areas after
nuclear disaster. PLos One. 2015;10(3):e0121990.
[22] Sakumi A, Miyagawa R, Tamari Y, Nawa K, Sakura
O, Nakagawa K. External effective radiation dose
to workers in the restricted area of the Fukushima
Daiichi nuclear power plant during the third year
after the Great East Japan Earthquake. J Radiat Res.
2016;57(2):178-181.
[23] Cardis E, Kesminiene A, Ivanov V, Malakhova I,
Shibata Y, Khrouch V, et al. Risk of thyroid cancer
131
after exposure of I in childhood. J National Cancer
Institute. 2005;97(10):724-732.
[24] Hamada N, Ogino H. Food safety regulations: what
we learned from the Fukushima nuclear accident. J
Environ Radioact. 2012;111:83-99.
[25] Hirakawa S, Yoshizawa N, Murakami K, Takizawa M,
Kawai M, Sato O, et al. Surveys of food intake just after
the nuclear accident at the Fukushima Daiichi nuclear
power station. Food Hyg Sci. 2016;58(1):36-42.
[26] Kim E, Kurihara O, Suzuki T, Matsumoto M, Fukutsu K,
Yamada Y, et al. Screening survey on thyroid exposurefor children after the Fukushima Daiichi nuclear power
station accident. Proc. of the first NIRS symposium onreconstruction of early internal dose in the TEPCO
Fukushima Daiichi nuclear power station accident.
National Institute of Radiological Sciences. Chiba,
Japan, July 2012. NIRS-M-252. 2012. p.59-66.
[27] Kim E, Kurihara O, Kunishima N, Momose T, Ishikawa
T, Akashi M. Internal thyroid doses to Fukushimaresidents – estimation and issues remaining. J Radiat
Res. 2016;57(s1):i118-i26.

J. Natl. Inst. Public Health, 67 (1) : 201817

Osamu Kurihara[28] Tokonami S, Hosoda M, Akiba S, Sorimachi A,
Kashiwakura I, Balonov M. Thyroid doses for evacuees
from the Fukushima nuclear accident. Sci Rep.
2012;2:507.
[29] Matsuda N, Kumagai A, Ohtsuru A, Morita N, Miura
M, Yoshida M, et al. Assessment of internal exposure
doses in Fukushima by a whole body counter within
one month after the nuclear power plant accident.
Radiat Res. 2013;179:663-668.
[30] Kamada N, Saito O, Endo S, Kimura A, Shizuma
K. Radiation doses among residents living 37 km
northwest of the Fukushima Dai-ichi nuclear power
plant. J Environ Radioact. 2012;110:84-89.
[31] Kim E, Kurihara O, Kunishima N, Nakano T, Tani
K, Hachiya M, et al. Early intake of radiocesium by
residents living near the TEPCO Fukushima Dai-ichi
nuclear power plant after the accident. Part 1: internal
doses based on whole-body measurements by NIRS.
Health Phys. 2016;111(5):451-464.
[32] Momose T, Takada C, Nakagawa T, Kanai K, Kurihara O,
Tsujimura N, et al. Whole-body counting of Fukushimaresidents after the TEPCO Fukushima Daiichi nuclear
power station accident. In: Proceedings of the first
NIRS symposium on reconstruction of early internal
dose in the TEPCO Fukushima Daiichi nuclear power
station accident. National Institute of Radiological
Sciences. Chiba, Japan, July 2012. NIRS-M-252. 2012.
p.67-82.
[33] Tsubokura M, Gilmour S, Takahashi K, Oikawa T,
Kanazawa Y. Internal radiation exposure after the
Fukushima nuclear power plant disaster. JAMA.
2012;15:669-670.
[34] Hayano RS, Tsubokura M, Miyazaki M, Satou
H, Masaki S, Sakuma Y. Inter nal radiocesium
contamination of adults and children in Fukushima 7
to 20 months after the Fukushima NPP accident asmeasured by extensive whole-body-counter surveys.
Proc Jpn Acad. Ser. B. 2013;89:157-163.
[35] Koizumi A, Harada KH, Niisoe T, Adachi A, Fujii Y,
Hitomi T, et al. Preliminary assessment of ecological
exposure of adult residents in Fukushima prefecture
to radioactive cesium through ingestion and inhalation.
Environ Health Prev Med. 2012;17:292-298.
[36] Harada KH, Fujii Y, Adachi A, Tsukidate A, Asai F,
Koizumi A. Dietary intake of radiocesium in adultresidents in Fukushima prefecture and neighboring
regions after the Fukushima nuclear power plant
accident: 24-h food-duplicate survey in December
2011. Environ Sci Technol. 2013;47:2520-2526.
[37] Sato O, Nonaka S, Tada J. Intake of radioactive
materials as assessed by the duplicate diet method in

18

Fukushima. J Radiol Prot. 2013;33:823-838.
[38] Yamaguchi I, Terada H, Kunigita N, Takahashi K. Doseestimation from food intake due to the Fukushima
Daiichi nuclear power plant accident. J Natl Inst Public
Health. 2013;62(2):138-143. (in Japanese)[39] World Health Organization. Preliminar y dose
estimation from the nuclear accident after the 2011
Great East Japan Earthquake and Tsunami. 2012.
[40] Murakami M, Oki T. Estimated dietary intake ofradionuclides and health risks for the citizens ofFukushima City, Tokyo, and Osaka after the 2011
nuclear accident. PLos One. 2014;9(11):e112791.
[41] Tsutsumi T, Nabeshi H, Ikarashi A, Hachisuka A,
Matsuda R. Estimation of the committed effective doseof radioactive cesium and potassium by the market
basket method. Shokuhin Eiseigaku Zasshi (Food Hyg.
Saf Sci). 2013;54(1):7-13. (in Japanese)[42] Hirokawa D, Omori S, Nishimura N, Yoshida K, Wada
I, Yamakoshi A. Survey on radioactive cesium andpotassium intake from food using duplicate diet (fiscal
year 2011-2014). Shokuhin Eiseigaku Zasshi (FoodHyg Saf Sci). 2016;57(1):7-12. (in Japanese)131[43] Kawai M, Yoshizawa N, Suzuki G. I dose estimationfrom intake of tap water in the early phase after
Fukushima Daiichi Nuclear Power Plant Accident.
Radiat Prot Dosimetry. 2017 (in press).
[44] Ohba T, Hesegawa A, Kohayagawa Y, Kondo H,
Suzuki G. Body surface contamination levels ofresidents under different evacuation scenarios after
the Fukushima Daiichi Nuclear Power Plant Accident.
Health Phys. 2017;117(3):175-182.
[45] Shinkarev SM, Kotenko KV, Granovskaya EO,
Yatsenko VN, Imanaka T, Hoshi M. Estimation of thecontribution of short-lived radioiodines to the thyroid
dose for the public in case of inhalation intake following
the Fukushima accident. Radiat Prot Dosimetry.
2015;164(1-2):51-56.
[46] J a pa n H e a lt h Phy s ic s So c iet y. Re p or t on t h eestablishment of standardization for direct
measurements. Expert committee report series.
2016;9(1).
[47] Fukushima Prefecture. Results of examinations forinternal exposure using whole-body counters. http://
www.pref.fukushima.lg.jp/site/portal/ps-wbc-kensakekka.html (accessed 2017-12-06) (in Japanese)[48] Hayano RS, Tsubokura M, Miyazaki M, Satou H, Sato
K, Masaki S, Sakuma Y. Comprehensive whole-bodycounter surveys of Miharu-town school children forthree consecutive years after the Fukushima NPP
accident. Proc Jpn Acad, Ser. B. 2014;6:211-213.
[49] Tsubokura M, Kato S, Nomura S, Morita T, Sugimoto

J. Natl. Inst. Public Health, 67 (1) : 2018

External and internal dose assessments of Fukushima residents after the 2011 nuclear disaster
A, Gilmore S, et al. Absence of internal radiation
contamination by radioactive cesium among children
affected by the Fukushima Daiichi nuclear power plant
accident. Health Phys. 2015;108(1):39-43.
[50] Taira Y, Hayashida N, Orita M, Yamaguchi H, Ide J,
Endo Y, et al. Evaluation of environment contaminationand estimated exposure doses after residents returnhome in Kawauchi village, Fukushima Prefecture.
Environ Sci Technol. 2014;48(8):4556-4563.
[51] Tsubokura M, Kato S, Nihei M, Sakuma Y, Furutani T,
Uehara K, et al. Limited internal radiation exposure
associated with resettlements to a radiationcontaminated homeland after the Fukushima Daiichi
nuclear disaster. PLos One. 2013;8(12):e81909.
[52] Tsubokura M, Kato S, Nomura S, Gilmour S, Nihei
M, Sakuma Y, et al. Reduction of high levels ofinternal radio-contamination by dietary intervention
in residents of area affected by the Fukushima Daiichi
nuclear power plant disaster: a case series. PLos One.
2014;9(6):e100302.
[53] Oughton D, Albani V, Barquinero F, Chumak V, Clero
E, Crouail P, et al. - on behalf of the SHAMISEN
Consortium. Recommendations and procedures for
preparedness and health surveillance of populations
affected by a radiation accident. 2017. https://www.
isglobal.org/documents/10179/5808947/SHAMISEN+
Recommendations+and+procedures+for+preparedn
ess+and+health+surveillance+of+populations+affe
cted+by+a+radiation+accident+EN/f3df29c3-1c004004-91fc-3b0750d5458e (accessed 2017-12-06)[54] Ishikawa T, Takahashi H, Yasumura S, Ohtsuru A,
Sakai A, Ohira T, et al. Representativeness of individual
external doses estimated for one quarter of residents
in the Fukushima Prefecture after the nuclear disaster:
the Fukushima Health Management Survey. J Radiol
Prot. 2017;37:584-605.
[55] N a t i o n a l I n s t i t u t e o f R a d i o l o g i c a l S c i e n c e s ,Japan Atomic Energy Agency. Researches on thecharacteristics of personal doses after the accidentof TEPCO Fukushima Daiichi nuclear power plant.
NIRS-M-270. 2014. http://www.nirs.qst.go.jp/
publication/irregular/02.html (accessed 2017-12-06) (inJapanese)[56] N a t i o n a l I n s t i t u t e o f R a d i o l o g i c a l S c i e n c e s ,Japan Atomic Energy Agency. Researches on thecharacteristics of personal doses after the accident
o f T E P C O Fu ku s h i m a D a i i c h i n u c l e a r p o w e rplantNadditional research. NIRS-M-276. 2015. http://
www.nirs.qst.go.jp/publication/irregular/02.html(accessed 2017-12-06) (in Japanese)[57] Yajima K, Kurihara O, Ohmachi Y, Takada M, Omori
Y, Akahane K, et al. Estimating annual individual
doses for evacuees returning home to areas affectedby the Fukushima nuclear accident. Health Phys.
2015;109(2):122-133.
[58] Satoh D, Furuta T, Takahashi F, Endo A, Lee C, Bolch
WE. Calculation of dose conversion coefficients forexternal exposure to radioactive cesium distributed insoil. JAEA-Research 2014-017. 2014. (in Japanese).
[59] Satoh D, Furuta T, Takahashi F, Lee C, Bolch WE.
Simulation study of personal dose equivalent forenternal exposure to radioactive cesium distributed insoil. J Nucl Sci Techonol. 2017;54(9):1018-1027.
[60] Adachi N, Adamovitch V, Adjovi Y, Aida K, Akamatsu
H, Akiyama S, et al. Measurement and comparison ofindividual external doses of high-school students living
in Japan, France, Poland and Belarus—the ‘D-shuttle’project—. J Radiol Prot. 2016;36:49-66.
[61] International Atomic Energy Agency. IAEA Safety
Standards, Criteria for use in preparedness andresponse for a nuclear or radiological emergency.
General Safety Guide No. GSG-2. 2011.
[62] Kim E, Kurihara O, Tani K, Ohmachi Y, Fukutsu K,
131
137
Sakai K, et al. Intake ratio of I to Cs derived fromthyroid and whole-body doses to Fukushima residents.
Radiat Prot Dosimetry. 2016;168(3):408-418.
[63] Hosoda M, Tokonami S, Akiba S, Kurihara O, Sorimachi
A, Ishikawa T, et al. Estimation of internal exposureof the thyroid to 131I on the basis on 134Cs accumulated
in the body among evacuees of the Fukushima
Daiichi nuclear power station accident. Environ Int.
2013;61:73-76.
[64] Morita N, Miura M, Yoshida M, Kumagai A, Ohtsuru A,
Usa T, et al. Spatiotemporal characteristics of internalradiation exposure in evacuees and first responders
after the radiological accident in Fukushima. Radiat
Res. 2013;180:299-306.
[65] Kunishima N, Kurihara O, Kim E, Ishikawa T, Nakano
T, Fukutsu K, et al. Early intake of radiocesium by
residents living near the TEPCO Fukushima Daiichi nuclear power plant after the accident. Part 2:
relationship between internal dose and evacuation
behavior in individuals. Health Phys. 2017;112(6):512525.
[66] Nakano T, Kim E, Tani K, Kurihara O, Sakai K. A
survey on the accuracy of whole-body counters
operated in Fukushima after the nuclear disaster.
Radiat Prot Dosimetry. 2016;170(1-4):100-102.

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Osamu Kurihara

2011 原子力災害後における福島住民の外部及び内部被ばく線量評価
栗原治
量子科学技術研究開発機構・放射線医学総合研究所

抄録
2011年 3 月11日に発生した東京電力福島第一発電所事故（福島原発事故）から既に 7 年間が経過し，これまでの間，主として福島県住民を対象とした個人線量測定及び評価が数多く行われてきた．言うまでもなく，住民に対する個人線量評価は，今後の放射線被ばくに起因する健康影響の評価を行う上で重要である．本稿では，これまでに報告された関連する日本人研究者による主要論文の概観を行う
ともに，福島原発事故に係る個人線量測定及び評価に係る経験や課題について記述した．福島県住民が同事故によって受けた全身の被ばく線量の推計値は総じて低く，自然放射線から受ける年間の被ばく線量と同等またはそれ以下とする論文が大半であった．現存被ばく状況下にある近年のきめ細かい
個人線量測定は，追加被ばく線量を低減するための方策を検討する上で有用であり，また，放射線リ
テラシーの醸成に貢献している．個人線量評価における残された大きな課題としては，特に事故初期の被ばく線量の不確かさの評価であり，さらなる研究が望まれる．
キーワード：福島第一原発，線量評価，外部被ばく，内部被ばく，原発事故，住民

20

J. Natl. Inst. Public Health, 67 (1) : 2018