WHO Thyroid Dose Estimation - PowerPoint Presentation

1. WHO Thyroid Dose Estimationfollowing the Fukushima Daiichi NPP accidentInternational Workshop on Radiation and Thyroid Cancer22 February, Tokyo, JAPAN

2. OutlineWHO's mandateFirst-year dose estimation (preliminary dose estimation report)Lifetime dose estimation (health risk assessment report)Discussion

3. World Health OrganizationFunction: act as the UN directing and coordinating authority on international health workObjective: "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)

4. Joint Radiation Emergency Management Plan (2010)

5. Health Risk AssessmentPurposeFulfil WHO's role and responsibilities under the Joint Radiation Emergency Management PlanProvide information for policy makers and health professionals in WHO Member States, as well as international organizationsGive an indication of the health implications of the accident

6. Risk CharacterizationHazard IdentificationDose-response RelationshipExposure AssessmentHealth Risk AssessmentThe classical stepsPublished 23 May 2012Exposure Assessment

7. Independent expertsLynn AnspaughMikhail BalonovCarl BlackburnFlorian GeringStephanie HaywoodJean-René JourdainGerhard ProehlShin SaigusaJane SimmondsIchiro Yamaguchiand other contributors listed in the report Observers:

8. Risk CharacterizationHazard IdentificationDose-response RelationshipExposure AssessmentHealth Risk AssessmentPublished28 February 2013Risk CharacterizationHazard IdentificationDose-response RelationshipExposure Assessment

9. Independent expertsMakoto AkashiBilly AmzalLynn AnspaughAnssi AuvinenNick GentPeter JacobDominique LaurierCharles MillerOtsura NiwaRoy ShoreRichard WakefordLinda WalshWei Zhangand other contributors listed in the report Observers:

10. ScopePreliminary dose estimationRadiation doses to the public for the first year following the accidentDoses characteristic of the average doses, assessed for different age groups in locations around the worldExcludesDoses within 20 km of the NPPDoses to workersHealth risks and public health actions

11. Locations in Fukushima Prefecture where dose might be higherThe rest of Fukushima prefecture (less affected)Other prefectures in JapanCountries neighbouring JapanOther regions of the world Geographical coverage

12. 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 adultsExposure through drinking tap water used in the preparation of infant formula was considered for 6 month old infantsFoetus and breast-fed infants not separately calculated but considered in the textThese age groups provide a sufficient level of detail to characterize radiological impact with consideration of younger, more sensitive populationDosimetric endpoints

13. Assessed exposure pathwaysIAEA report on Environmental consequences of the Chernobyl accident and their remediation: twenty years of experience (2006)

14. General approachAs 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 measurementsThe dose estimation was based on data available up-to mid September 2011, and extrapolations were used to calculate the first-year dose

15. Technical annexes

16. Dose assessment inside JapanExternal and InhalationInput 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

17. Dose assessment inside JapanIngestionDoses estimated by WHO on the basis of measurements of radioactivity concentrationMonitoring of food originating in Japan (both as marketed in Japan and in foods exported from Japan) received/compiled by WHO through its INFOSAN networkFood consumption survey (2009) provided by the Japanese National Institute for Health and Nutrition (NIHN)

18. 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 measuresAssumptionsIngestion doses inside Japan

19. AssumptionsConsideration of protective actionsMovement 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 monthsStable iodine: it was assumed that KI tablets were not taken in Japan nor elsewhereFood 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

20. ResultsThyroid doses

21. 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

22. Considerable variation in environmental monitoringVariability of human behaviour patterns and locationsAir concentrations based on deposition measurementsInhalation dose estimates cautiously assume the iodine was in elemental vapour formDegree of shielding provided by housingUse of ICRP dose coefficients for Japanese populationSource term…..Sources of uncertainties

23. Validation of resultsHuman measurementsComparisons with in vivo human measurementsThyroid monitoring of >1,000 children in Fukushima between 24 and 30 March 2011Whole body monitoring on 3,373 Fukushima residentsMonitoring 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 RNonly consider internal exposure (not external)

24. Health risk assessmentThe Lifetime Attributable Risk (LAR) for different cancer types requires the dose to the affected organ over the lifetimeThe 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

25. Example of annual dose distribution

26. Thyroid doseGeneral PopulationThe 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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29. Exposure of emergency workersData were provided by TEPCO for 23,172 workers up to March 2012: TEPCO workers (24%) and contractors (76%)

30. Thyroid doseEmergency workersFour exposure scenarios assumed~ 66% of workers; total effective dose of 5 mSv~ 33% of workers; total effective dose 30 mSv< 1% of workers; total effective dose of 200 mSv2 workers with total effective dose of 700 mSv and high thyroid doses due to 131I intake

31. Organ doses Scenarios for emergency workers

32. ConclusionsEffective doses were very low outside Japan and in much of JapanEffective doses are estimated to be less than 50 mSv in Fukushima prefectureThyroid doses were mainly received during the first year and were highest in the most affected areasUnlike other organs, the thyroid doses for infants were estimated to be nearly twice compared to adultsThe 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 incidentComparison with human measurements gives confidence that the estimated results were not under-estimating the doses in Japan