Transcript Slide 1

Salient features of the forthcoming
ICRP recommendations-2007
Dr. Pushparaja
Ex. Head, Radiation Hazards
Control Section, RSSD, BARC
(Based on the ICRP approved draft recommendations
-2007 (13/2/2007)
www.radsafetyinfo.com
Since 1990 Recommendations
New biological and physical information
New trends in setting and presentation of
radiation protection standards
Societal changes leading to more
emphasis on the protection of individuals
and stakeholders in the management of
radiological risk
More emphasis on the radiological
protection of non-human species.
The major features
Updating the radiation and tissue weighting
factors and radiation detriment
Maintaining the commission’s three fundamental
principles: justification, optimization and
application of dose limits
Abandoning the process-based approach and
moving to situation-based approach and
applying the same source-related principles to
all controllable exposure situations-planned,
emergency and existing exposure situations.
Continued….
Maintaining the existing individual dose limits for
effective dose and equivalent dose from all
regulated sources. These represent the
maximum dose that would be accepted in
planned situations by the regulators.
Principle of optimization is applicable to all
exposure situations with restrictions on
individual doses (dose constraints) for planned
exposures and reference levels for emergency
and existing exposure situations.
Developing a framework for radiological
protection of non-human species.
Source is any physical quantity
or procedure that results in
potentially quantifiable
radiation dose to a person or
group of persons.
Types of harmful effects
(ICRP-99, 2006)
Radiological protection deals with two
types of harmful effects:
Tissue reactions (deterministic effects)
Incidence of cancer or hereditary effects
(stochastic effects)
For protection, action at
Source
Environmental pathways
Exposure
Dose to individuals
The aims of the
recommendations
To contribute to an appropriate level of
protection for people and the environment
against the detrimental effects of radiation
exposure without unduly limiting desirable
human endeavours and actions that may
be associated with such exposures. The
recommendations are based on the
scientific knowledge and expert
judgements.
Objectives of the system
radiological protection
For humans: To mange and control
exposures to ionizing radiation so that
tissue reactions are prevented and risks of
cancer and heritable effects are
minimized.
For environment: Control exposures to
ensure negligible impact
Basis
The system of protection of humans is based on
the use of:
Reference anatomical and physiological models
for assessment of radiation doses
Biological studies at the molecular and cellular
level
Experimental animal studies on mechanisms of
carcinogenesis and heredity
Epidemiological studies
Principles of radiological protection
The two principles which are source-related
and applicable to all situations are:
Justification – to achieve an individual or
societal benefit that is higher than the
detriment it causes.
Optimization of protection – to maximize
the margin of benefit over harm; ALARA.
Continued…
Application of dose limits
Individual-related, and applies to planned
exposure situations. Total dose should not
exceed the limits. Not applicable to medial
exposures, public exposures in emergency
situations and to existing exposure situations.
The limits are same as those given in ICRP-60,
1991.
The scope of the
recommendations
Applies to all radiation sources, both
natural and man-made, and
controllable exposures from any
source or sources regardless of its size
and origin. Also applies to all radiation
exposure situations.
System of radiation protection of
humans
Commission moves from the earlier
process based approach to the following
three types to address all conceivable
types of exposure situations:
Planned
Emergency, and
Existing exposure
Planned Exposure situations
Radiological protection can be planned in
advance, before exposure occursmagnitude and extent of the exposure can
be reasonably predicted, cover medical
exposure of patients, comforters and
carers, all categories of exposure can
occur, also covers potential exposures,
which may result from deviations from the
normal operating conditions, safety and
security of sources is the issue of concern
Emergency exposure situations
Unexpected situations requiring urgent protective actions to
be implemented.
Exposure scenario is complex
Response actions can be planned to some extent
Actual emergency situations are unpredictable
To be optimized using a chosen reference levels (20-100
mSv band)
Overall dose from the possible multiple pathways, with no
protection action employed is called as Projected dose
(ICRP-101, 2006)
Protection strategy to reduce residual dose level below the
reference dose
Integrate radiation emergency response plan into all-hazards
emergency management program
Existing exposure situations
Type of existing exposure situations where exposures
can be high enough to warrant radiological protective
actions are:
Radon in dwellings/workplaces
NORM residues
Residues in the environment due to emissions
from past operations
Contaminated territories resulting from accidents
Linear non-threshold model
Commission assumes that at doses below 100
mSv in a year, the increase in the incidents of
stochastic effects with a small probability and in
proportion to the increase in radiation dose over
the background dose and hence, the LNT model
is the best practical approach for managing risk
from low dose radiation exposure.
ICRP recommends LNT model combined with a
dose and dose arte effectiveness factor
(DDREF) for extrapolation from higher doses for
radiological protection at low dose and low dose
rates (ICRP-99, 2006).
Levels of radiological protection
An individual exposed to several sources;
exposures identified and quantified; include all
exposures from regulated sources - called
individual-related approach.
Considering the exposures of all the individuals
exposed by each regulated source – sourcerelated approach.
Appropriate level of protection is achieved
by optimization using dose constraints and
reference levels
Categories of exposures
Occupational exposure
Operating management and Licensee
responsible for the safety
Public exposures
All exposures other than occupational and
medical exposures incurred as a result of
a range of radiation sources, natural and
man-made
Medical exposures of patients, comforters
and carers (separate guidance provided)
Exposed individuals
Workers
Has recognized rights and duties in relation to
occupational radiological protection.
Pregnant workers not to avoid work, can work in
designated areas; should not be involved in
emergency actions involving high radiation
doses; treated like members of the public.
Additional equivalent dose to the fetus would not
exceed 1 mSv during the reminder of the
pregnancy.
Continued….
Members of the public
A large number of different natural and manmade sources is contributing; Dose restrictions
are applied to the mean dose in the appropriate
critical group.
Critical group concept is replaced by “The
representative person” (Pub: 101, 2006); Typical
habits of individuals in a representative group in
the most exposed, are used.
Continued…
Patients, comforters, carers
Individuals, who receives an exposure
from diagnostic, therapeutic and screening
procedures, which are justified and
optimized. Dose limits/constraints not
applicable. To use diagnostic reference
levels. (ICRP-73, 1996)
Dose constraints (in planned exposure
situations) and Reference levels (in
emergency and existing situations) are
used for protection of members of the
public or workers from a single source
in all exposure situations (Sourcerelated restriction).
These are used in conjunction with
optimization of protection to assure
ALARA
Dose constraint/Reference levels
Dose constraints can be defined as a level
of dose above which it is unlikely that
protection is optimized for a give source
and therefore action must always be taken
to bring the level of dose below the
constraint.
Reference levels represent the dose or
risk above which it is judged to be
inappropriate to plan to allow exposures to
occur and below which optimization should
be implemented.
Due to multiplicity of the sources,
sole reliance on source-related
restrictions may not provide the
required level of protection.
Restriction on the sum of the
doses from the sources is
required; this individual-related
restriction is called – Dose Limit
Optimization
It is the principle of protection with a
restriction on individual dose is the central
to the system of protection applying to all
the three exposure situations, planned,
emergency and existing.
Meaning to:
To keep likelihood of incurring exposures,
the number of people exposed and the
magnitude of individual doses ALARA
below the dose constraints or reference
levels, taking into account economic and
societal factors.
Optimized protection is the result
of an evaluation, which balances
the detriment (economic, human,
societal, political) and the
resources available for protection
of individuals. Best option need
not necessarily the one with the
lowest dose.
Uncertainties
In view of the uncertainties in the estimate of
detriment and the value of tissue weighting
factors, the ICRP considers it appropriate to
use age and sex averaged tissue weighting
factors and numerical risk estimates, for
radiological protection purposes.
For the purpose of retrospective evaluation
of radiation related risks such as
epidemiological evaluations, and for the
evaluation of exposure risk of over-exposed
cases, age and sex-specific data should be
used.
Sex averaging
It is useful to determine a single value of
effective dose for both sexes. The tissue
weighting factors are sex averaged values and
are valid for the male and female breast, testes
and ovaries taken together in the value for the
gonads, and other organs and tissues with
assigned explicit Wt values. The effective dose
is computed from the weighting factor multiplied
by the arithmetic mean of the equivalent dose
assessed for organ or tissue T of the male, and
female including the remainder tissues.
Nominal risk estimates
ICRP’s risk estimates are called
nominal because they relate to the
exposure of a nominal population of
females and males with a typical age
distribution and are computed by
averaging over age groups and both
sexes. Effective dose is the
dosimetric quantity recommended for
radiological protection. Use absorbed
dose in known exposure scenarios.
Nominal Risk Coefficients
Risk of hereditary effects continues to be
included in the Commission’s system of
radiological protection. Post 1990 human
and animal data on the quantitative
aspects of radiation-induced germ cell
mutation and the fundamental
understanding of the human genetic
diseases indicated that the risk of heritable
disease was overestimated in the past.
Continued…
The newly estimated hereditary risks employing
human and mouse studies and in view of the
lack of clear evidence in human of germ line
mutations caused by radiation (in demonstrable
genetic effects in offspring), works out to be
0.2% per Sv.
This value relates to continuous low dose-rate
exposure over these two generations (UNSCEAR2001: NAS/NRC-2006)
The judged value for tissue weighting factor for
gonads is considerably reduced.
Detriment – adjusted nominal risk
coefficients for cancer and hereditary effects
Sex-averaged nominal risk coefficients for
cancer involves the estimation of normal risks for
different organs and tissues followed by
adjustment of these risks for lethality and quality
of life and the derivation of a set of site-specific
values of relative detriment.
This includes heritable effects from gonadal
exposure. These relative detriments form the
basis for the new tissue weighting factors.
Continued……….
The ICRP detriment was based on
fatal cancer risk weighted for nonfatal cancer, relative life lost for fatal
cancers and life impairment for nonfatal cancers.
Radiation weighting factors
(ICRP-92, 2003)
Radiation type
Photons
Electrons & Muons
Protons & Charged
Pions
Alpha, FF & Heavy
Ions
Neutrons
(Continuous function of
neutron energy)
Radiation Weighting
Factor
1
1
2
20
2 to 20
Recommended Tissue Weighting
Factors
Tissue
WT
Bone marrow, colon, lung,
Stomach, Breast, Remainders
(13 organs/tissues)
0.12
Gonads
0.08
Bladder, Oesophagus, Liver,
Thyroid
0.04
Bone surface, Brain, Salivary
glands, Skin
0.01
Nominal Risk Coefficients (% per Sv)
Publication 60
ICRP-2007
Whole population
Whole population
Cancer
Heritable
Total
Cancer
Heritable
Total
6.0
1.3
7.3
Adult
Adult
Cancer
Heritable
Total
5.5
0.2
6.0
4.8
0.8
5.6
Cancer
Heritable
Total
4.1
0.1
4.0
Collective dose concept
Collective dose takes into account the group of
persons exposed and the period of exposure from
a source. The collective effective dose (man
sievert) is retained as an instrument for optimization
purpose only, for comparing radiological
technologies and protection procedures, not for risk
projections. Commission recommends avoidance of
computation of cancer deaths using collective
doses involving trivial exposures over extended
periods to large populations. The dose calculations
should have limiting conditions of the dose range
and the time period (ICRP-77/81 (1998/2000).
Continued….
Each exposure situation must be carefully
analyzed to identify the individual
characteristics and exposure parameters that
best describe the exposure distribution
among concerned population. In the decision
taking process, less weight should be given
to very low doses and to doses received in
the distant future since the doses and sizes of
exposed population becomes increasingly
uncertain as time increases.
ICRP defined bands of Dose
constraints/ Reference levels
0.01 to 1 mSv
Benefit to society; Planned operation
of practices with marginal increase in
exposures above natural background;
Provides rigorous level of protection
by direct action on the source;
periodic checks. Ex: Constraints set
for public exposure.
Continued…
1 mSv – 20 mSv
Individuals get direct benefit from an exposure
situation not necessarily from the exposure;
Individual monitoring, training; constraints set
for occupational exposure in planned
situations, exposure involving high levels of
natural background radiation; Exposure
control by action at the source or at the
exposure pathways. Ex: Constraints set for
Occupational exposure in planned situations;
Reference levels for radon in dwellings
Continued….
20 to 100 mSv
Projected dose over a time period; Total dose
from all the sources; Source can not be
controlled; extreme situations where actions
taken to reduce exposures are disruptive such
as in radiological emergency; acute exposures
not expected to be repeated. Important:
Selection of an appropriate value for the
reference level is the necessary and important
for protection, whatever the situation.
Medical exposure of patients
Medical exposure covers:
The exposure of individuals for
diagnostic, fluoroscopically guided
interventional, and therapeutic
purposes
Family members, friends supporting
and comforting patients
Volunteers in biomedical research
Ensure that
Doses to patient dose to be commensurate
with the medical purpose
Avoid unnecessary / unproductive doses in
intervention procedures (ICRP-85/87/93;
2000,2000, 2003)
Avoid exposure of healthy tissues in
radiotherapy (ICRP-44, 1985)
ICRP-73, 1996 recommendations remain
valid, Also: the documents SG-2, 2001 &
ICRP-2007.
Radiation effects in the embryo and fetus
At doses below 100 mGy of low LET radiation
Lethal effects of irradiation in the preimplantation period of embryonic development is
very infrequent.
Radio-sensitivity maximum during the period of
major organogenesis
Animal data indicates a true dose threshold of
100 mGy for the induction of malformation.
A-bomb survivor data supports a true dose
threshold of at least 300 mGy for severe mental
retardation after irradiation. Any effect on IQ
following in-utero doses under 100 mGy is of no
practical significance (ICRP-90, 2003)
Unjustified medical procedures
Addition of activity in commodities and
consumer products
Radiological exposures for any purpose
without any clinical evaluation of the
images / clinical indication
Mass screening of population groups
unless for detecting diseases and its
control if detected.
Some guidance levels
Termination of pregnancy not considered below
absorbed dose of 100 mGy
Above this level, informed decisions taken.
Dose constraint of 5 mSv per episode for carers and
comforters (ICRP-94, 2004)
Avoid contamination of infants, children and pregnant
women
No special restrictions for small exposures received in
public transport, waiting rooms and permanently
implanted sealed sources (ICRP-98, 2005)
Cremation of bodies: 12 months since implantation of I125; 3 months for Pd-103)
Bio medical research: Ethics Committee to decide dose
constraints
Continued….
Justification falls on the government
The key parameter for the control of existing
situations is TIME.
Optimization process to reduce individual doses
to below reference levels (1 to 20 mSv, the
projected dose)
Protection strategies, implementation of the
actions and monitoring of the effectiveness
Radon
A strong correlation between residential radon exposure and
risk of lung cancer as shown by the residential case-control
studies (UNSCEAR-2006)
National authorities to set national reference level for
optimization of protection.
Retains the upper value of 10 mSv as individual dose
reference level (ICRP-65) and corresponding activity
concentration of 1500 Bq per cubic meter for workplaces and
600 Bq per cubic meter for residential dwellings
Optimized level for occupationally harmonized value = 1000
Bq per cubic meter (suggested by Commission)
Exposures to radon below the national reference level
should not be regarded as part of the occupational exposure.
Radiological Protection of the
Environment
Need is felt for internationally acceptable
policy, advice and guidance to assess the
impact of radiation exposures on the
environment and the radiological protection
aspects. A comprehensive and systematic
approach is being developed (ICRP-91,
2003). The Commission is setting out data
for some reference animals and plants
(hypothetical entities with certain assumed
basic biological characteristics), and intends
to offer more practical advice in the future.