Radiation Risks at Low Doses - Nuclear Awareness...

Centre for Radiation, Chemical and Environmental Hazards

Radiation Risks at Low Doses

Nuclear Awareness Meeting, July 2009

John Harrison

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Topics

• Sources of information

• Cancer risks

• Internal cf. external

• Protection system

• Concerns / research

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Sources of information

UNSCEAR Reports on doses and effects

Science

ICRP Recommendations

Policy

UN, EU Basic Safety Standards

Regulations

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Sources of information

• Epidemiological studies

• Experimental studies

• Modelling

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Epidemiology

• ‘A’ bomb survivors

• Nuclear workers

• Patients

• Chernobyl

• Radon – mines/houses

• Radium exposures

• Plutonium workers

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Experimental studies

• Dose-response

• Radiation type: α, β, γ

• Acute/chronic

• Radionuclides in the body

• Mechanisms

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Key facts

• Easy to measure

• Can kill

• Can cause cancer

• All exposed

• Well understood

• Sophisticated system of control

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Radiation Health Effects

Dose (mSv)

Proba-bility

1000

Certain(100%)

Clinically observ-able in individuals

100? 50?

Bur

ns, r

adia

tion

sick

ness

& d

eath

Increasing risk of cancer

Disease statistics for populations (epidemiology)

Statistical limit of epidemiology

Biologi-cally

plausible

Chernobyl firemenChernobyl child

thyroid dosesNatural background,

occupational, radwaste

Limit of pathology

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Cancer risks from external radiation

Hiroshima and Nagasaki ‘A’ bomb survivors

UK National Registry of Radiation Workers(NRRW)

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Cancer risks from external radiation

‘A’ bomb survivors44,635 with > 5 mGy, 7851 solid cancers 1958-98, 11% attributable

NRRW174,541 with average dose 25 mSv

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Leukaemia in the NRRW & ‘A’ bomb survivors

Figure 1 Trends with dose in relative risk (and 90% CI) for mortality from leukaemia excluding CLL

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.1 0.2 0.3 0.4 0.5 0.6

Dose (Sv)

Rela

tive

risk

NRRW point estimates NRRW linear f itNRRW linear f it Low er NRRW linear f it Upper BEIR VII Leukaemia mortality BEIR VII Low erBEIR VII Upper

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Solid cancers in the NRRW & ‘A’ bomb survivors

Figure 2 Trends with dose in relative risk (and 90% CI) for mortality from all malignant neoplasms excluding leukaemia

0.9

1

1.1

1.2

1.3

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6

Dose (Sv)

Rela

tive

risk

NRRW point estimates NRRW linear f it NRRW linear f it Low er

BEIR VII All Solid NRRW linear f it Upper BEIR VII All Solid Upper

BEIR VII All Solid Low er

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Age-specific cancer risks

Cases per 106 exposed to a single dose of 10 mGy (BEIR VII)

Cancer site Age at exposure, yearsMales Females

0 20 60 0 20 60Breast - - - 1171 429 31Colon 336 173 94 220 114 62Liver 61 30 14 28 14 7Lung 314 149 89 733 346 201Thyroid 115 21 0.3 634 113 1Leukaemia 237 96 82 185 71 57All cancers 2563 977 489 4777 1646 586

- life-time attributable risk forU.S. population

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Radium dial painters

In U.S., almost 5000 employees mainly women mainly from 1915 – 1954

Bone sarcomas

Head sinus carcinoma

Not leukaemia

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Mayak Pu production

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Mayak Pu exposures

High exposures to Pu in late 1940s, early 1950s

Lung, liver and bone cancersLeukaemia related to external radiation, not Pu

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Leggett et al (2005) biokinetic model for Pu

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Urinary excretion of Pu

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05

Time after intake (d)

Dai

ly e

xcre

tion

(% in

ject

ed a

ctiv

ity p

er d

ay)

ICRP 67Leggett et alLP 45yNRPB dataAEAT dataLangham dataMayak estimate

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Bone structure

Trabecular boneRed bone marrow

Endosteum

Cortical bone

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Alpha emitter on bone surface

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Yin et al J. Clin. Invest.116, 1195-1201 (2006)

Location of haemopoieticstem cells

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Cancer risk estimates for alpha emitters

• Radon Lung cancer

• Thorotrast Liver cancer &Leukaemia

• Radium isotopes Bone cancer

• Plutonium-239 Lung (liver & bone cancer)

Harrison and Muirhead J. Radiat. Biol. 79, 1-13 (2003)

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Linear non-threshold (LNT)dose response

Dose

Rad

iation C

ance

r Ris

k

~100 mGy

?

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Constraints, reference levels, limits

Protection of workers and public primarily using constraints and reference levels applying to doses from a single source

Constraints / reference levels Limits

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Constraints, reference levels

ProspectiveDose

reject options

Constraint/Reference level

acceptable options

Optimisation

Constraints and reference levels are an integral part of optimisation

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Constraints, reference levels

Societal benefit (not individual). No information, training or individual monitoring. Assessment of doses for compliance.

1 mSv or less

Individual direct or indirect benefit. Information, training and either individual monitoring or assessment.

Greater than 1 - 20 mSv

Exceptional situations. Benefit on a case-by-case basis. Information, training and individual monitoring of workers, assessment of public doses.

Greater than 20 - 100 mSv

CHARACTERISTICS AND

REQUIREMENTS

BANDS OF PROJECTED DOSE

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Average Annual Dose to UK population - 2.7 mSv

16%ARTIFICIAL

42000

84% NATURAL

0.1% products0.2% fallout0.2% occupational

50% radon gas from the ground

13% gammarays from ground and

buildings15% medical12% cosmic

rays

9.5% from foodand drink

<< 0.1% discharges

42000

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Radioactivity in Food and the Environment, 2007

HPA advice:0.15 for new nuclear build

0.01Cardiff

0.5 (0.2)Sellafield

< 0.005Aldermaston

mSvCritical group doses

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Childhood leukaemia clusters

• Kinderkrebs der Umgebung von Kernkraftwerken (KIRK) study showed excess in < 5 y with 5 km of German reactors

• Similar studies in UK and France do not show excess

• Excesses near Sellafield and Dounreay cannot be explained by radiation

• Childhood leukaemias do cluster – largest in USA near Fallon Naval Air Station

• Population mixing and infections – Kinlen hypothesis

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Concerns

• Medical exposures

• Radon

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Gift Certificates for RadiationExposure

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Radon

HPA advice on the Limitation of Human Exposures to Radon

Consultation until 3 September 2009

Reduce UK Action Level ?

Change designation of affected areas ?

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Research

• Epidemiology, including internal emitters, cardiovascular disease

• Mechanisms at low doses

• Uncertainties

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Key facts

• Easy to measure

• All exposed

• Cancer risks quantified

• Sophisticated system of control