Draft ICRP Recommendations Peter Burns ARPANSA

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Draft ICRP RecommendationsPeter BurnsARPANSA

• 15th PBNC - October 2006

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ICRP 2006 Recommendations

• ICRP Publication 60
• Recommendations of the International Commission
  on Radiological Protection, 1990.
• Widely adopted internationally - Basis for the
  IAEA BSS
• Draft Recommendations of the International
  Commission on Radiological Protection - 02/276/06
  - 5 June 2006.

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ICRP 2006 Recommendations

• The ICRP has decided to issue revised
  recommendations having three primary aims in
  mind
• To take account of new biological and physical
  information and of trends in the setting of
  radiation safety standards
• To improve and streamline the presentation of the
  recommendations and
• To maintain as much stability in the
  recommendations as is consistent with the new
  scientific information.

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ICRP 2006 Recommendations

• Foundation documents
• Biological and Epidemiological Information on
  Health Risks Attributable to Ionising Radiation
  (C1)
• Basis for Dosimetric Quantities Used in
  Radiological Protection (C2)
• Building blocks
• Low-Dose Extrapolation of Radiation-Related
  Cancer Risk (C1)
• Radiological Protection in Medicine (C3)
• Optimisation of Protection (C4)
• Assessing Dose to the Representative Individual
  (C4)
• The Scope of Radiological Protection Regulations
  
• Exclusion and Exemption (MC)

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ICRP RP 06 - Major Features

• Maintaining the fundamental principles of
  radiological protection, and clarifying how they
  apply to sources and the individual
• Updating the weighting factors and the radiation
  detriment
• Maintaining the dose limits
• Extending the concept of constraints in the
  source-related protection to all situations.

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Why the need for change?

• The Commission emphasises that it is not a change
  but a clarification of the existing system, which
  has its origin over 50 years ago
• In London in 1950 ICRP recognised that the world
  of radiation protection had changing

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Changes in radiation protection

• Development of nuclear reactors and nuclear
  weapons in the 1940s led to
• Atmospheric weapons tests
• Nuclear power
• Artificial radioisotopes for medicine and
  industry
• These developments meant a greater potential for
  wide scale exposures of populations

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Changes in radiation protection

• By 1950 there was clear evidence that
• cumulative doses from chronic exposure had caused
  leukaemia in radiologists
• hereditary effects had been demonstrated in
  animals

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Changes in radiation protection

• Long term cumulative exposures were significant
  for carcinogenic and hereditary effects
• The probability of developing these effects was
  proportional to cumulative doses
• Previously limits had been designed to prevent
  superficial effects by keeping exposures below a
  rate of 1 R per week

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ICRP - London 1950

• ICRP lowered exposure rate from 1R w-1 to 0.3R
  w-1
• "While the values proposed for the maximum
  permissible exposures are such as to involve a
  risk that is small compared to the other hazards
  of life, nevertheless in view of the
  unsatisfactory nature of much of the evidence on
  which judgements are based, coupled with
  knowledge that certain radiation effects are
  irreversible and cumulative, it is strongly
  recommended that every effort be made to reduce
  exposures to all types of ionizing radiations to
  the lowest possible level."

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Evolution of recommendations

• 1950 as low as possible
• 1958 as low as practicable
• 1966 readily achievable, economic and
  social considerations.
• 1973 reasonably achievable
• 1976 economic and social factors

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ICRP 60 - 1990

• In 1960 the Commission introduced the concept of
  Optimisation to sit with Justification and
  Limitation as the main principles for radiation
  protection
• Dose Constraints were introduced as benchmarks
  in the Optimisation Process
• There has been much confusion about what Dose
  Constraints are and how to apply them and the new
  recommendations are attempting to address this

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DRAFT ICRP Recommendations

• The General System of Radiological Protection
• The probabilistic nature of stochastic effects
  means a clear distinction between 'safe' and
  'dangerous is impossible.
• Fundamental principles are
• Justification, Limitation and Optimisation.
• Dose Constraints in the Optimisation Process are
  the primary tool in managing radiation safety.

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Additional Radiation Dose and Risk
UNACCEPTABLE RISK
DOSE LIMIT
TOLERABLE RISK
DOSE CONSTRAINT
Optimisation
Protection optimized
ACCEPTABLE RISK
TRIVIAL RISK
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DRAFT ICRP Recommendations

• The General System of Radiological Protection
• Strong radiation safety culture through a cycle
  of continuous review and assessment to optimise
  doses for practices using a single source.
• Optimisation involves evaluating and
  incorporating measures that tend to lower doses
  to the public and workers.
• It also entails consideration of avoidance of
  accidents and other potential exposures.

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DRAFT ICRP Recommendations

• Dose constraints are used as an integral part of
  the process of prospectively optimising
  radiological protection at the source.
• If an assessment shows a relevant constraints was
  not complied with,
• further consideration of protection options in
  an optimisation procedure is required,
• this should not necessarily be regarded as a
  failure of protection.

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DRAFT ICRP Recommendations

• It is the process of prospectively optimising
  radiological protection that is important
• Constraints should be set according to well
  managed practices and should be monitored and
  modified if necessary
• Reference or Action Levels - Level of Ambition
• It is not about compliance with a number

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Application of Dose Constraints

• The optimisation of protection is a forward
  looking iterative process aimed at preventing
  exposures before they occur.
• Operators and the appropriate national
  authorities have responsibilities for applying
  the optimisation principle.
• Optimisation of protection is the responsibility
  of the operating management, subject to the
  requirements of the authority.
• An active safety culture supports the successful
  application of optimisation by both the
  operational management and by the authority.

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Application of Dose Constraints

• All aspects of optimisation cannot be codified
  optimisation is more an obligation of means than
  of results.
• The authority should focus on processes,
  procedures and judgements rather than specific
  outcomes.
• An open dialogue must be established between the
  authority and the operating management to ensure
  a successful optimisation process.

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DRAFT ICRP Recommendations

• Three exposure situations are identified
• Planned Situations are everyday situations
  involving the planned operation of practices.
• Emergency Situations are unexpected situations
  that occur during the operation of a practice
  requiring urgent action.
• Existing Situations are exposure situations that
  already exist when a decision on control has to
  be taken, including natural background radiation
  and residues from past practices.

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DRAFT ICRP Recommendations

• For planned situations
• constraints represent a basic level of
  protection
• In emergency or existing controllable exposure
  situations
• constraints represent a level of dose or risk
  where action to reduce that dose or risk is
  almost always warranted.

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Band of Projected Effective Dose0.01 - 1 mSv -
Acute or Annual

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Band of Projected Effective Dose1 to 20 mSv -
Acute or Annual

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Band of Projected Effective Dose20 to 100 mSv -
Acute or Annual

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ICRP Radiation Protection 06

• Minor changes to
• Radiation weighting factors
• Tissue weighting factors
• Risk coefficients
• Caution on the use of
• Effective Dose
• Collective dose

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Main Conclusions on Biology

• Dose-response for stochastic effects A simple
  proportionate relationship between dose and risk
  at low doses.
• DDREF 2.
• Genomic instability, bystander effects, adaptive
  response Still insufficient knowledge for
  protection purposes.
• Genetic susceptibility Known disorders too rare
  to distort risk estimates impact of weak genetic
  determinants cannot be judged.
• In-utero cancer risk Life time risk similar to
  that of young children (a few times higher than
  that of the whole population).

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Main Conclusions on Biology

• Nominal probability coefficients for cancer
  Based on incidence and not mortality.
• Nominal probability coefficients for heritable
  diseases Based on UNSCEAR 2001
• - up to 2nd generation
• Tissue reactions in adults Revised judgements
  but no major changes.
• Risks of non-cancer diseases (A-bomb LSS) Great
  uncertainty on dose response below 1 Sv no
  judgement on low dose risk possible.

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Radiation Weighting Factors, wR
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Tissue Weighting Factors

• Determine lifetime cancer incidence risk for
  radiation associated cancers.
• Apply DDREF.
• Transfer risk estimates across populations
  (ERREAR weights).
• Apply weighted risk estimates to and average
  across seven Western and Asian populations to
  provide nominal risk coefficients.
• Adjust for lethality, quality of life and for
  years of life lost to obtain the radiation
  detriment for each type of cancer.
• Normalize to unity and obtain the relative
  radiation detriments.
• Group into four categories broadly reflecting the
  relative detriments, i.e. the tissue weighting
  factors.

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Tissue Weighting Factors, wT
1 Nominal wT divided equally between 14 tissues.
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Nominal Risk Coefficients for Stochastic Effects
( Sv-1)
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Use of Effective Dose (E)

• E is calculated by using reference values for a
  reference person or group. Weighting factors are
  averaged over age and gender.
• E should be used only for compliance of
  constraints and dose limits to control stochastic
  effects.
• E should mainly be used for planning in
  prospective situations.
• E should not be used for more detailed
  retrospective dose and risk assessments on
  exposure of individuals.
• E should not be used for epidemiological studies.
  

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Use of Collective Dose

• Is an instrument for optimisation, for comparing
  radiological technologies and protection
  procedures.
• Is not intended as a tool for epidemiologic risk
  assessment. It is therefore inappropriate to use
  it in risk projections based on epidemiological
  studies.
• The computation of cancer deaths based on
  collective doses involving trivial exposures to
  large populations is not reasonable and should be
  avoided. Such a use was never intended and is an
  incorrect use of the collective dose.

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UNSCEAR 2006 Report

• United Nations Scientific Committee on the
  Effects of Atomic Radiation
• 2006 Report to be submitted to the General
  Assembly on 25 October

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UNSCEAR 2006

• 5 Annexes on biological effects of radiation
• Sources-to-effects assessment for radon in homes
  and workplaces
• Epidemiological studies of radiation and cancer
• Epidemiological evaluation of cardiovascular
  disease and other non-cancer diseases following
  radiation exposure
• Effects of ionizing radiation on the immune
  system
• Non-targeted and delayed effects of exposure to
  ionizing radiation