r.v. osborne 1 are the proposed recommendations of the international commission on radiological...

R.V. Osborne 1

Are the Proposed Recommendations of the International Commission on

Radiological ProtectionTaking Us in the Right Direction?

Richard V. Osborne

Robert S. Landauer, Sr. Lecture49th Annual Meeting of the Health Physics Society

Washington, DC, 2004 July 11-15

PL1.1

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The Right Direction . . .

“. . .if you don’t know where you are going, chances are you will end up somewhere else.”

Yogi Berra

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What do we hope to be able to say of the new recommendations?


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Changes are evolutionary, not revolutionary.

Science base is sound.

Concepts, quantities, and vocabulary are clear.

Role of justification is clear.

Application of limits and constraints is clear.

Misuse of collective dose is avoided.

Categories of exposure are more helpful.

System is linked to mainstream risk assessment and management.

Recommendations are accepted as authoritative.


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How do the draft recommendations measure up against this vision?


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Draft ICRP 2005 Recommendations

Stated aims:

Consolidate and clarify decade of ICRP recommendations.

Remain consistent with other international guides and standards.

Suggests intent is evolutionary, not revolutionary.

Move from a utilitarian approach to protection to one based on the individual.

Taken as a given that this is right - should be challenged.

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The Right Direction . . .?

Consider here under the headings:

Science base

Quantities and concepts

Principles: Justification Dose limits and constraints Optimisation of protection

Application

Environment

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Science base

Deterministic effects …………...Tissue/organ reactionsDetailed analysis of current literature.

Conclude: No thresholds for tissue reactions below tens of mGy.

Stochastic effects………………..Cancer development Heritable disease

Key question: Does the current epidemiological and experimental body of knowledge lead to a different model?

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Science base

ICRP considered:Epidemiological evidenceComplex nature of radiation-induced DNA damageAdaptive responseGenomic instabilityBystander signalling . . .

Concluded: Despite extensive body of evidence, uncertainties too great to judge influence on low dose cancer rate.

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Science base

“. . . for the purposes of radiological protection, the Commission judges that the weight of evidence on fundamental cellular processes supports the view that in the low dose range up to a few tens of mSv, it is scientifically reasonable to assume . . . for practical purposes cancer risk will rise in direct proportion to absorbed dose . . .”

ICRP 2005, para. 101

This is a key assumption:Allows sources of exposure to be controlled independently.Protection concepts and quantities remain valid.

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Radiation protection quantities

Equivalent dose = Wr x Average absorbed dose

(sievert) (gray)

Effective dose = Wr x Wt x Average absorbed dose

(sievert) (gray)

Radiation weighted dose (??????)

(Operational quantity “Dose equivalent” remains)

Wr

Wt

Values adjusted

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Changes in radiation weighting factors wr

Protons…………..Reduced from 5 to 2Neutrons…………< 1Mev, reduced by 50%

Implications*

Nuclear power plant workplace spectrum

Reduction in wr by 23%

(c.f. ICRP26 to ICRP60, increase of 55%)

* A. Waker, private communication

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Tissue weighting factors wt and nominal risk coefficients:

Based mainly on the Life Span Study (incidence data).

Same value for the Dose and Dose Rate Effectiveness Factor (DDREF) as in ICRP 60.

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Quantities and conceptsTissue weighting factors wt

Gonads 0.20

Bone marrowColonLungStomach

0.12

BreastBladderLiverOesophagusThyroid

SkinBone surface

0.01

Remainder 0.050.05

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Gonads 0.20

Quantities and conceptsTissue weighting factors wt

Bone marrowColonLungStomach

0.12

BreastBladderLiverOesophagusThyroid

SkinBone surface

0.01

Remainder 0.050.05

Gonads

Gonads 0.20

BreastBladderLiverOesophagusThyroidGonads

0.05

Breast

BrainKidneySalivary glands

Remainder

(Applied to averagedose to 14 tissues)

0.050.1

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Slight reduction in detriment coefficients (%/Sv):Whole population 7.3Adult workers 5.6

6.54.9

Caveat on effective dose and nominal risk coefficients.

Don’t use for:Estimating risks retrospectively for individuals.Epidemiological purposes with populations.

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Principles: Justification

Acknowledges radiological considerations may be only minor part of justification of practices.

Justification of radiation-related medical procedures remains important principle within the scope of radiological protection.

“More good than harm to patient and account taken of detriment to staff and others.”

Appears to be a helpful clarification.

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Principles: Dose Limits and Constraints

Adapted from ICRP2005

Dose Limit

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Adapted from ICRP2005

Dose Constraint

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ICRP 60 values of the dose limits are retained.

Limits continue to be used for the level of protection for individuals “from all regulated sources only in normal situations.”

Dose constraints are much more important:“ . . . the fundamental level of protection . . . where action to avert exposures and reduce doses is virtually certain to be justified.”

Quantified for all “controllable situations”Normal sourcesExisting exposuresEmergencies

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Natural radiation background: “a benchmark for judgement about . . . relative importance [of added exposures] and the need for action.”

Basis for recommended maximum values for dose constraints

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Recommended maximum values for dose constraints on single sources

100Emergencies, evacuations, no justification above

20 Some benefits to exposed individuals

1Societal rather than individual benefit0.01Minimum value

Incremental dose

mSv in a year

Natural background (1 mSv/a)

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Four values of dose constraints selected to be consistent with the current scheme.

Still need variety of constraints for variety of circumstances.

More detailed consideration of types of public exposure would help.

Helpful in countering the idea that the same “limit” has to apply in every situation.

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Dose constraints not explicitly related to nominal risk.

For potential exposures and “risk constraints” need to cite risk associated with dose constraint.

Annual constraints or one-off?

Basis for limits was life-time risk.

Constraints are expressed as annual doses.

Fundamental change in basis for control.

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Comparison with natural background:

Attempts to combat exaggeration of significance of low doses.

Exaggerates the significance of more than a few mSv

May be misapplied as justifying (or not) particular exposures.

Weak basis for the “fundamental” control levels.

Diminishes the science base.

May reduce credibility.

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Comparison with natural background:

Unintentional message may be:

“There is concern about doses above natural background.”

rather than

“The effect on health of low doses of radiation is overwhelmingly likely to be zero.”

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Principles: Optimisation of Protection

Complements constraints.(Importance seems to be reduced.)

Emphasis is on protecting individuals.(Societal or utilitarian aspects are downplayed.)

Optimisation is said to be broader than “ALARA”.

“ . . . protection and safety issues receive the attention warranted by their significance.”

“ . . . consideration of the avoidance of accidents and other potential exposures”

“The involvement of stakeholders . . . is an important input . . .”

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Principles: Optimisation of Protection

Optimal protection results when: “exposures to individuals . . . represent the best choice in the the prevailing circumstances.”

Exposures in workplace should be “ALARA, social and economic factors taken into account.”but . . .Control of emissions should be “best available technology not entailing excessive costs . . . with due consideration to social and economic factors.”

“ALARA” could be said to include all these.

No caveats on stakeholder involvement.

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Principles: Optimisation of ProtectionSteers away from using collective dose as such in the protection of groups.

The “dose matrix” idea:Number of exposed individualsMagnitude of individual dosesDose distribution in timeAge- and sex-dependent modifiersEquity considerationsReal or potential exposures

Not clear what the underlying principle is.

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ICRP seem to be caught between two maxims:


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“We must adjust to changing times and still hold to unchanging principles.”

President Jimmy Carter


“It is a terrible thing to look over your shoulder when you are trying to lead - and find no one there.”

President Franklin D. Roosevelt

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Application

System of protection applies to “controllable sources”“ . . . either the source of exposure or the pathways leading to the doses received by individuals can be controlled by some reasonable means.”

Not a clear definition.

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Application

alpha emitters 0.01 Bq/g beta/gamma emitters 0.1 Bq/g

uranium-238/thorium-232 1 Bq/gpotassium-40 10 Bq/g

Exclude from the system of protection:Cosmic rays at ground level, potassium-40 in bodyArtificial radionuclides (low end of internationally-exempted concentrations).

Natural radionuclides (high end of natural range).

Confusion of exclusion and exemption.Values may preclude higher exemption values for particular purposes.Simple screening approach might be better.

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Environment

Responding to criticism that previous position not substantiated:

“ . . . protect man . . . protect environment . . .”

Adopts principles as developed by IAEA (sustainability, biodiversity, habitat protection . . .).

Aims for consistency with human protection.

“ . . . radiation levels where action is needed and with explicit reference to natural background dose rates.”

Implicitly suggests concern at few times natural background?This seems much too restrictive.

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Environment

Suggest developing “reference biota”dosimetry modelsenvironmental geometrieslife cycle biologypathways to exposure

Useful basis for deriving “ambient activity levels”.

Overall system of protection to parallel that for people.

May be better to aim for closer harmonisation with current environmental protection practice.

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Are the Proposed Recommendations of the

International Commission on Radiological Protection

Taking Us in the Right Direction?

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The Right Direction?

Interpretation of science………………………………..yes

Terminology and concepts……………………………. yes/no

Adjustment of quantities………………………………. yes

Clarification of “Justification” …………………………. yes

Emphasis on dose constraints rather than limits…… yes but . . . basis of annual natural background……….. no

Emphasis on broad-based optimisation……………... yes but . . . advice on implementation…………………... no

continued . . .

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Excluded activity concentrations……………………... maybe

Development of tools for biota protection…………….yes but . . . framework development…………………….. no

Evolutionary not revolutionary………………………... yes but . . . overall direction……………………………… no

Consultative process…………………………………... yes

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Review and comment by the end of 2004

www.icrp.org

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