radiation risks at low doses - nuclear awareness...
TRANSCRIPT
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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