Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan1 |

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 |

Outline

WHO's mandate

First-year dose estimation (preliminary dose estimation report)

Lifetime dose estimation (health risk assessment report)

Discussion

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan3 |

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)

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan4 |

Joint Radiation Emergency Management Plan (2010)

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Health 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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan6 |

Risk Characterization

Hazard Identification

Dose-response Relationship

Exposure Assessment

Health Risk AssessmentThe classical steps

Published 23 May 2012

Exposure Assessment

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan7 |

Independent expertsLynn AnspaughMikhail BalonovCarl BlackburnFlorian Gering

Stephanie HaywoodJean-René Jourdain

Gerhard ProehlShin Saigusa

Jane SimmondsIchiro Yamaguchi

and other contributors listed in the report

Observers:

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan8 |

Risk Characterization

Hazard Identification

Dose-response Relationship

Exposure Assessment

Health Risk Assessment

Published

28 February 2013

Risk Characterization

Hazard Identification

Dose-response Relationship

Exposure Assessment

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan9 |

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:

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan10 |

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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan11 |

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 coverage

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan12 |

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 endpoints

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan13 |

Assessed exposure pathways

IAEA report on Environmental consequences of the Chernobyl accident and their remediation: twenty years of experience (2006)

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan14 |

General 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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan15 |

Technical annexes

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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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan17 |

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)

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan18 |

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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan19 |

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

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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 uncertainties

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan23 |

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)

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan24 |

Health 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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan26 |

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

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan27 |

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan28 |

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan29 |

Exposure of emergency workers

Data were provided by TEPCO for 23,172 workers up to March 2012:

– TEPCO workers (24%) and contractors (76%)

Radiation and Thyroid Cancer Workshop, February 2014, Tokyo, Japan30 |

Thyroid doseEmergency workers

Four exposure scenarios assumed1. ~ 66% of workers; total effective dose

of 5 mSv2. ~ 33% of workers; total effective dose

30 mSv3. < 1% of workers; total effective dose

of 200 mSv4. 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

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Conclusions 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