radiation and thyroid cancer workshop, february 2014, tokyo, japan 1 |1 | who thyroid dose...
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Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan1 |
WHO Thyroid Dose Estimationfollowing the Fukushima Daiichi NPP accident WHO Thyroid Dose Estimationfollowing the Fukushima Daiichi NPP accident
International Workshop on Radiation and Thyroid Cancer
22 February, Tokyo, JAPAN
Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan2 |
OutlineOutline
WHO's mandate
First-year dose estimation (preliminary dose estimation report)
Lifetime dose estimation (health risk assessment report)
Discussion
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World Health Organization World Health Organization
Function: act as the UN directing and coordinating authority on international health work
Objective: "the attainment by all peoples of the highest possible level of health"
Definition: "HEALTH is a state of COMPLETE physical, mental and social well-being and not merely the ABSENCE of disease or infirmity" (Constitution, 1948)
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Joint Radiation Emergency Management Plan (2010)
Joint Radiation Emergency Management Plan (2010)
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Health Risk AssessmentHealth Risk Assessment
Purpose Fulfil WHO's role and responsibilities
under the Joint Radiation Emergency Management Plan
Provide information for policy makers and health professionals in WHO Member States, as well as international organizations
Give an indication of the health implications of the accident
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Risk Characterization
Hazard Identification
Dose-response Relationship
Exposure Assessment
Health Risk AssessmentThe classical steps
Health Risk AssessmentThe classical steps
Published 23 May 2012
Exposure Assessment
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Independent expertsLynn AnspaughMikhail BalonovCarl BlackburnFlorian Gering
Stephanie HaywoodJean-René Jourdain
Gerhard ProehlShin Saigusa
Jane SimmondsIchiro Yamaguchi
and other contributors listed in the report
Observers:
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Risk Characterization
Hazard Identification
Dose-response Relationship
Exposure Assessment
Health Risk AssessmentHealth Risk Assessment
Published
28 February 2013
Risk Characterization
Hazard Identification
Dose-response Relationship
Exposure Assessment
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Independent expertsMakoto Akashi
Billy AmzalLynn AnspaughAnssi Auvinen
Nick GentPeter Jacob
Dominique LaurierCharles MillerOtsura NiwaRoy Shore
Richard WakefordLinda WalshWei Zhang
and other contributors listed in the report
Observers:
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ScopePreliminary dose estimation
ScopePreliminary dose estimation
Radiation doses to the public for the first year following the accident
Doses characteristic of the average doses, assessed for different age groups in locations around the world
Excludes– Doses within 20 km of the NPP– Doses to workers– Health risks and public health actions
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Locations in Fukushima Prefecture where dose might be higher
The rest of Fukushima prefecture (less affected)
Other prefectures in Japan
Countries neighbouring Japan
Other regions of the world
Geographical coverageGeographical coverage
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Effective doses and equivalent doses to the thyroid for the first year after the accident in:
– 1 year old infants, 10 year old children and adults– Exposure through drinking tap water used in the
preparation of infant formula was considered for 6 month old infants
– Foetus and breast-fed infants not separately calculated but considered in the text
These age groups provide a sufficient level of detail to characterize radiological impact with consideration of younger, more sensitive population
Dosimetric endpointsDosimetric endpoints
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Assessed exposure pathwaysAssessed exposure pathways
IAEA report on Environmental consequences of the Chernobyl accident and their remediation: twenty years of experience (2006)
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General approachGeneral approach
As far as possible, doses were based on environmental measurements (ground, soil, food….)
Primary source of measurement data for Japan was provided by the Government of Japan
Where data were insufficient, modelling was used based on an estimated source term in combination with environmental measurements
The dose estimation was based on data available up-to mid September 2011, and extrapolations were used to calculate the first-year dose
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Dose assessment inside JapanExternal and Inhalation
Dose assessment inside JapanExternal and Inhalation
Input data based on measurements published by MEXT (Ministry of Education, Culture, Sports, Science and Technology in Japan) (http://radioactivity.mext.go.jp/en/)
Doses estimated by the Russian Institute of Radiation Hygiene (IRH) and by the German Federal Office of Radiation Protection (BfS)
Similarities/differences in the methodologies discussed in the report
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Dose assessment inside JapanIngestion
Dose assessment inside JapanIngestion
Doses estimated by WHO on the basis of measurements of radioactivity concentration
Monitoring of food originating in Japan (both as marketed in Japan and in foods exported from Japan) received/compiled by WHO through its INFOSAN network
Food consumption survey (2009) provided by the Japanese National Institute for Health and Nutrition (NIHN)
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All people in Fukushima prefecture consumed only food produced in Fukushima prefecture (possible dose overestimation)
Losses due to radioactive decay between the point of food ‘marketing’ and the time of consumption not included, neither are losses due to food preparation and losses during cooking
Food sourcing and normal food distribution practices likely to have been significantly altered by the impact of the tsunami, the earthquake, and public protection measures
AssumptionsIngestion doses inside Japan
AssumptionsIngestion doses inside Japan
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AssumptionsConsideration of protective actions
AssumptionsConsideration of protective actions
Movement of people– < 20km radius: not considered (people evacuated)– 20-30 km: not specific considerations for sheltering– "Deliberate evacuation zone": the assessment assumed relocation
at 4 months
Stable iodine: it was assumed that KI tablets were not taken in Japan nor elsewhere
Food and water restrictions: the assessment does not explicitly model the effect of the imposition of food and water restrictions, it is implicit since the assessment is based on monitoring results reported by the GoJ
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ResultsThyroid doses
ResultsThyroid doses
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For the populations that were relocated, it was assumed that people stayed there up to 4 months and then moved to the least contaminated zones of Fukushima prefecture
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Considerable variation in environmental monitoring Variability of human behaviour patterns and locations Air concentrations based on deposition measurements Inhalation dose estimates cautiously assume the iodine was in
elemental vapour form Degree of shielding provided by housing
Use of ICRP dose coefficients for Japanese population
Source term
…..
Sources of uncertaintiesSources of uncertainties
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Validation of resultsHuman measurements
Validation of resultsHuman measurements
Comparisons with in vivo human measurements– Thyroid monitoring of >1,000 children in Fukushima between 24 and 30 March
2011– Whole body monitoring on 3,373 Fukushima residents– Monitoring of citizens coming back from Tokyo (France and Germany);
monitoring of citizens living in Tokyo (Russia)
In vivo measurements may be regarded as broadly in accordance with the dose assessment, considering
– "snapshots" at a particular time: do not include intakes that may have place later over the 1st year and/or short-lived RN
– only consider internal exposure (not external)
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Health risk assessmentHealth risk assessment
The Lifetime Attributable Risk (LAR) for different cancer types requires the dose to the affected organ over the lifetime
The ratio of lifetime dose to first-year dose was assumed to be 2, based on Chernobyl experience and taking into account differences with the Fukushima accident
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Example of annual dose distribution Example of annual dose distribution
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Thyroid doseGeneral Population
Thyroid doseGeneral Population
The approach used to calculate lifetime doses for the other organs (i.e. ratio lifetime dose/first-year dose equal to 2) was only applied to the component of the thyroid dose due to external exposure from the ground
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Exposure of emergency workersExposure of emergency workers
Data were provided by TEPCO for 23,172 workers up to March 2012:
– TEPCO workers (24%) and contractors (76%)
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Thyroid doseEmergency workers
Thyroid doseEmergency workers
Four exposure scenarios assumed1. ~ 66% of workers; total effective dose
of 5 mSv
2. ~ 33% of workers; total effective dose 30 mSv
3. < 1% of workers; total effective dose of 200 mSv
4. 2 workers with total effective dose of 700 mSv and high thyroid doses due to 131I intake
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Organ doses Scenarios for emergency workers
Organ doses Scenarios for emergency workers
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ConclusionsConclusions Effective doses were very low outside Japan and in much of Japan
Effective doses are estimated to be less than 50 mSv in Fukushima prefecture
Thyroid doses were mainly received during the first year and were highest in the most affected areas
Unlike other organs, the thyroid doses for infants were estimated to be nearly twice compared to adults
The doses estimated in the example locations of Fukushima prefecture may be somewhat overestimated:
– Relocation of residents assumed at 4 months (some were relocated earlier);
– Other protective measures only partially taken into account, due to lack of more detailed information
– Dominant exposure pathways were inhalation and external exposure early after the incident
Comparison with human measurements gives confidence that the estimated results were not under-estimating the doses in Japan