The 2nd Asian Regional Conference on the Evolution of the System of Radiological Protection

The new ICRP System of Radiological Protection
Roger Clarke, ICRP Chair(2004/07/28 Tokyo)

Thank you chairman, good morning colleagues, it is my honor to have been invited here, and I’m
extremely grateful to my good friends in the NEA for facilitating the meetings which have taken
forward our ideas on the new recommendations. I would also like to thank Dr. Oda andCommissioner Kusumi for their personal welcome. I am grateful and I take note of what was said,
and, since I am a native English speaker, I will be simple, clear, and easy to understand. Sorry
Commissioner. (Joke)
The draft recommendations, now, are meant to represent an evolution in our presentation ofradiological standards, not a revolution. The science has evolved since the last recommendations
were made in 1990, and societal expectations have progressed since 1990, so this is what leads us toour 2005 recommendations. The recommendations will be supported by a number of foundation
documents. And we hope that the 2005 recommendations will, perhaps, be Publication 100, I do not
know, Publication 1 was in 1959, as was already said. The issues which are covered in therecommendations include the quantitative, use of radiological protection, which will be subject to afoundation document, a supporting document, prepared by Committee II. The biological aspects,
which include the work on the nature of the dose response relationship, and the risk factors, will becovered by two reports from Committee I. So,
our recommendations will describe the generalsystem of protection that we now are evolving,the quantitative, or numerical values that werecommend, followed by how we now see
optimisation being undertaken. We deal withmedical exposures, potential exposures,
exclusion to try and clarify the difference
between exemption from regulatory control andexclusion from consideration in any way. And,
finally, we address protection of theenvironment.
So, let us start with the various issues, and the first is on the dosimetric side, where we arecontinuing to use the quantity effective dose. There are some changes taking place, as you know, inthe development of voxel phantoms, rather than the old MIRD phantoms, the old mathematicalphantoms. The changes to effective dose are basically, firstly, there are new values of the radiation
weighting factor following a review of the RBE data and those considerations are in Publication 92.
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The major changes are reductions, a reductionin the radiation weighting factor for protons, ofall energies from 5 to 2. This, I emphasise, isthe result of a review of the RBE data. For
neutrons of energies less than 1 MeV, again
there is the reduction, by about a factor of two,in the recommended values for neutrons lessthan 1 MeV. And the radiation weighting
factors are applied to the external incident
neutron fluence and the neutron spectrum isdegraded as it passes through the body.
And so there is an increasing contribution from gamma rays to the deeper organs. The net result isthat we recommend a reduction in the factor. We also propose new values of tissue weighting factors,
following a review which will be published by Committee I, a review of the risk data for somatic andhereditary defects. As you well know, because the 2001 UNSCEAR Report, the risk of hereditarydisease is now significantly less, in our estimates, than previously. So the radiation weighting factors,
here we see on the first. In Publication 60 we recommended a histogram for incident neutron energy,
we gave a function which is Curve B on theslide, and now, for the reasons that I haveoutlined, with regard to the degradation of thespectrum of the neutrons through the body, you
see the new function, Curve C, which
represents low energies, about a reduction of 2
in the radiation weighting factor. And, forcalculational convenience, we express it inmathematical terms at the bottom of the slide
there.
Now for the tissue weighting factors, you will find some of this work described in Annex A of thedraft recommendations. The highest tissue weighting factor had been previously assigned to the
gonads. As a result of the review of the data, thegonad weighting factor has been reduced. We
have tried to keep the numerical values of thetissue weighting factors as they were in
Publication 60 and only make the minimumchanges. The evidence for risk to the female
breast suggests that we should increase thetissue weighting factor which we have done
there so that the breast now appears in thehighest grouping of organs with a weighting
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factor of 0.12. Skin and bone surface stay with their existing weighting factor, but Committee I feelsthat there are some other organs and tissues where the risks are small, but quantified, which should
be added to this group, and that includes the brain, kidney and salivary glands. We now give more,
an increased tissue weighting factor, to the remainder because Committee I feels that there are anumber of organs and tissues for which the risks are small, uncertain, but should be included in thesystem.
So, if we go on to the next slide, theremainder weighting factor of 0.1 is averaged
equally over 14 organs and tissues which I havelisted here and I apologise that the small
intestine here has been abbreviated, I hope you
have all of the others. Now the point perhaps tomake here, is that now in this formulation,effective dose becomes an additive quantity. In
the past, ever since effective dose has been
introduced, it has not been able to add theeffective dose from exposures to different
radioisotopes or fields, because the remainder was treated as being the 5 organs receiving the highest
dose in a list of remainder tissues.
So, between, the intake of one radionuclide, for example cesium 137, and the intake of anotherradionuclide plutonium 239 for example, in each case the identified root 5 remainder tissues would
be different. So when there would be a combined intake of cesium 137 and plutonium 239, together,
then there would be different set of 5 remainder tissues receiving the highest dose. So the effective
dose from an intake of cesium 137 could not be added to the effective dose from the intake ofplutonium 239. You have to do a new calculation. We have removed that difficulty; one step towards
simplicity. We now have a linear system and I think that it is a step forward.
Let me go on to the biological aspect and talk about the induction of tissue reactions. Again, forsimplicity, and for ease of translation, we are now speaking not of deterministic effects, the word
deterministic is ambiguous, it is used indifferent ways by ICRP and I am sure thatmany of us know the reactor accident
consequences are frequently performed in a
deterministic manner, as opposed to aprobabilistic manner. So, even ICRP was using
the word deterministic in different ways. Now
we speak of tissue reactions and again, to beclear, we want to ensure that when we arelooking at tissue reactions people do not use

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effective dose. Effective dose is meant for protection purposes where you do not expect threshold
effects, tissue reactions, and again, for clarity and simplification, we are now proposing that thequantity is a gray equivalent, we will use that name for tissue reactions, to avoid confusing people
about effective doses. It is a weighted absorbed dose, gray equivalent; it really means the absorbed
dose being multiplied by the relevant RBE for the tissue reaction. I might just mention at this pointthat we also are trying to avoid the confusion in translation about the radiation weighted effective
dose. I have been asked many times to explain the difference between equivalent dose and dose
equivalent. Apparently native English speakers find it easy, but translating that expression, or thoseexpressions, have proven difficult. So now we are going to speak about the radiation weighted dose
and we would like to have a new unit, the unit will be joules per kilogram, but we would like to giveit a name other than sievert, Sv, to avoid the confusion with the special name sievert being used for
effective dose. So in the same way the special name here is the gray equivalent, Gy-Eq. That is ICRP
trying to be helpful, clearer, and easier to translate. So for the other effects, the cancer, the reportcovers and the foundation documents from Committee I will cover the mechanisms of ontogenesis,
review the results of the epidemiological studies, consider specifically the embryo and the fetus, andany genetic predisposition to cancer induction following radiation exposure.
Hereditary defects, which I have already mentioned, following the UNSCEAR 2001 Report andfinally we will consider non-cancer diseases, although I can tell you that the conclusion from
Committee I is that the evidence on the non-cancer diseases is not sufficient to incorporate any
allowance in recommendations. For the detriment coefficient, again as a result of this work we again
see a reduction. The estimate of detriment for a population of all ages is now about 10% lower than it
was in 1990, largely because of the reduction in the estimate of hereditary defect. But also because
the estimate of fatal cancer probability is also 10% lower than in 1990. And what Committee I hasdone here is to come up with a new definition of detriment which you will find in therecommendations, in Annex A, and they havecommenced their calculations by using cancer
incidence data as opposed to the mortality data
used previously. They believe that the incidence
data is more certain than the old mortality data
and then they allow for a mortality fraction,
they allow for a loss of life, and they allow for
the loss of quality of life from hereditarydefects. And, putting all these things together,
we end up with both a fatal cancer nominal
probability coefficient and a detriment estimate,both of which are lower than we used before. This is very reassuring because it means that ourstandards essentially may remain, because there is no reason to think that we were under-protecting,not sufficiently protecting, workers and the public.
So the 2005 system of protection starts by explaining the principle of justification, followed by our4quantitative recommendations, the numerical restrictions on individual doses, and followed by theprinciple of optimisation this time, because whenever you optimise you need some sort of restriction
on the maximum individual dose to undertake an optimisation. That was said in Publication 60, butnever pursued.
So, let us start with justification, the justification of controllable sources and justifying the fact that
there is an overall benefit is the responsibility of national authorities, it is not for the ICRP.
Radiological considerations are only one input. I have been asked many times to justify practices
which occur in some countries but not in othercountries. But it is not for ICRP to justify thesepractices. A country may decide allow apractice for a number of reasons: strategic
reasons like trying to get a proportional energy
supply secure from oil fluctuations on the
global market, for economic reasons, fordefense reasons, for medical reasons, and forsafety reasons. Individual countries may maketheir own decisions that there is positive benefit
and it is not for ICRP to justify why a particular defense activity utilises radiation and gives rise toradiation exposures. Radiological considerations are an input but are not usually the determining
feature and ICRP recommendations can only apply when the government and the regulatory bodies
have declared the practice justified. And we also apply our recommendations to those natural sources
which are controllable. And, as we will see later, patient exposures need separate consideration. So
our new 2005 system then moves from the justified practices to the quantitative recommendations.
Now here I need to explain some conceptual points. The public is protected from a single source ofionising radiation in all situations, normal operations, emergency situations, in controllable exposure
situations that is where there is an existing source of exposure which can be controlled. In all
situations you are going to optimise protection and in order to perform an optimisation you need aconstraint. You constrain the exposure from a single source. That is what you tell the designer of a
facility. That is what you tell the designer to achieve. The constraint, the maximum dose that you aregoing to allow from that single source incomparison and of course what we have had in
the past has been the concept of dose limits
which protect the public from all the regulated
sources but only in normal operational
conditions. So the limits are what you tell thedesigner that he should use to design the
maximum effluence or maximum dose to the
public from a single source. Any one of thesesources, whether it is the radiology department5

of a hospital, whether it is a power station, or a mine, in each case the regulator will authorise
operation against a discharge or fluence from that single source facility. And that is the constraint; theconcept was introduced in Publication 60 but was never developed by ICRP. So the constraint to the
optimisation equally applies in non-normal situations.
Similarly for the worker, the worker isprotected from a single source, the worker in
the industry, the worker in the hospital,
protected from any single radiation source in all
situations by the relevant constraint, whereas
the worker is equally protected from all
occupational sources by the dose limits, but
only in normal operations. You cannot use thedose limit to design a facility because there areother sources. You cannot monitor the publicagainst the dose limit because you do not know
the origin of all sources of exposure. What you do is check individual sources, to comply with theirauthorised limits, their authorised releases, i.e., the authorized levels at which to operate. And theseauthorised levels are the results of applying constraints. I am sure you will have questions, but this is
not a revolution, this is an evolution. The concept was introduced in Publication 60 and not
developed. Now we are developing it to be useful, more useful to the regulator, more useful toindustry, more clarification, more simplicity, easier to translate. So, on the next slide, let us look at
the quantitative recommendations, and theprinciple recommendations that we areproviding this time are of course the constraints.
The restrictions that are established for the most
exposed individuals are figures which can be
set internationally and used by national
regulators. So, constraints, we see being set by
ICRP, and on the next slide we want to havefewer numerical values than we have had in thepast.
If you have read what we have previously written, since 1990 we have advised the use of nearly30, different numerical restrictions on individual dose in different circumstances. We would like toreduce those numbers but the reduced values will be numerically the same as some existing ones so
as to achieve continuity. We want to try and explain them in terms of multiples or fractions of theirnatural background radiation, which I believe, and we believe, can be simple to explain to people, topoliticians, members of the public, others who need to have explained to them the standards ofprotection, And, as I said before, constraints are required, they are a necessary criterion, but not a
sufficient criterion, for protection, which means that after you have sufficiently protected the most6

exposed individuals you must achieve a higher level of protection while optimising protection fromthe source. And it is the source from which you optimise protection. It is not all sources, so you need
the constraint and not the limit. So, constraints can be explained in terms of multiples or fractions of
the natural background. When using the natural background we have excluded radon, because weregard radon as technologically enhanced exposure or a manmade source of exposure. That is
because the indoor levels of radon are of magnitude of level higher than the outdoor levels and we
make recommendations to control radon at home and at work. So it is excluded from the inescapable
natural background which we used to compare
and above that natural background increasingly
ICRP would see sources giving rise to higher
doses, increasingly needing action. And there isa high need for action when doses get to be of
the order of 100 milli sieverts per year.
Similarly, before the natural background, ICRP
sees a decreasing need for action with sources
giving doses below 100 milli sieverts per yearwith a very low need for action when we getdown to as little as 10 micro sieverts per year. Now, basically, this is the scheme we see as a way of
explaining our need for action. The actions we have taken have been, in the past, derived as a wholevariety of bases, but now we think we can explain it in terms of their background. So let us move on
to our maximum constraints.
The maximum constraints we have suggested is 100 milli sieverts in a year, a 100 milli sieverts isa figure where we still believe we can use effective dose. And it is a number which you will find in
ICRP documents dealing with emergencies. So it is the maximum dose which we think you shouldplan for emergency workers other than those voluntarily undertaking lifesaving actions. It is the
maximum value that ICRP has suggested for relocation or evacuation of the public in emergency
situations and it is the level where we have recommended it is virtually certain to take action toprotect people from existing high levels of controllable exposure. So, this number, or numbers very
like it have been used for workers, for the public, for emergencies, for normal situations, for existing
situations, and we characterize this highest constraint as one where there are really not any individual
or societal benefits for individual exposures greater than this. You do not want people to receive
higher doses. And if you think people might receive higher doses than they are informed about therisks, about the doses and the circumstances in which they might receive them, they receive training
and they are monitored directly or their doses are assessed. And if you think about it, this is true forworkers, it is true for members of the public who may be affected by an accident, they are informed– you assess the doses. So we see here a common constraint which is almost 100 times background,
it is a number that has been used before, it is in the Basic Safety Standards, it is in ICRP documents.
But now we can just use one number rather than a series of numbers derived in different ways.
Our second constraint is 20 milli sieverts in a year, it is recommended in Publication 60 as the7maximum constraint from a single source forworkers, but we have also recommended
similar numbers for simple countermeasures
such as sheltering of the public or the
distribution of stable iodine in emergency
situations. We have a very similar number that
we have used for radon indoors, at home and atwork. We have used a number for comforters
and carers of patients undergoing treatment
with radionuclides. And here we characterize
this group as one in which there is a direct or an
indirect benefit to the individuals who are exposed and they are informed, they receive some training,
and there is some monitoring or assessment of the dosage. If it is a comforter for a patient, you assessthe dose that carer or comforter receives. What I want to emphasise is that we have used this figureof about 10 times the natural background as a level where we want to take action for workers, innormal situations, for the public in emergencies, for workers and the public for existing exposures –such as radon and for people involved with patients undergoing therapy. We have used a series ofrationale to arrive at the number, but the basic observation is that at the end of the day we have anumber that is about 10 times the background.
Our third constraint again recommended in Publication 60 and maintained here for continuity, is 1
milli sievert per year and the key thing is this could apply in situations where there is a societal
benefit but not necessarily individual direct benefit; it is where there may be an imposed burden. So
it applies in normal situations, you generally do not inform people about this, they are not trained andyou do not assess individual doses. You may monitor the environment.
And lastly, we have the value of 0.01 milli sieverts in a year, or 10 micro sieverts in a year, which
we say is the minimum constraint that should ever be applied. There is no justification, in our view,for trying to set a restriction on an individual source lower than 10 micro sieverts. You may still
apply the system of protection but you do not attempt to get the dose lower.
These are the constraints: radon, I said, wastreated separately and since in Publication 65
we established a system which seems to havebeen adopted all around the world, we now seethat what we have done in Publication 65 was
to set constraints on the radon source, where
action is almost certainly warranted, we did notdescribe it as a constraint but we now see thatconceptually it is a constraint, it is the most thatyou are prepared to let a worker or a member of8the public receive. It was derived on the basis of an exposure leading to dose of about 10 millisieverts in a year, and we said that these were the activity concentrations of radon, or the constraints
which regulatory authorities should start with and apply. The national authority optimizes protectionand establishes a lower level where at work you do not take the exposures into the system ofprotection. Radon exposures below these levels are not subject to the system of protection. And, athome, you do not try to reduce the levels further. So you end up by deriving a level at which you takeaction which will be a national level, because the optimised result of considering action against radon
will be different in a Scandinavian country, say Finland, in comparison with England, thecircumstances, the situation, is different. So the result will be different. But, ICRP can express
internationally the standards on which the regulators will start.
So now our quantitative recommendations
also include the individual limits. The
individual limits already exist in the Basic
Safety Standards and they are there to protect
workers and the public against all the regulated
sources in normal situations – but only innormal situations. And we see no reason tochange the dose limit. And you know that forthe public there is exceptionally a 5 year
averaging allowed. We maintain the averaging
that we recommended in Publication 60 for workers that the dose limit is 20 milli sieverts per year
averaged over 5 years as long as no more than
50 milli sieverts in a single year, which explains
why we can have a constraint for a single
source of 20 milli sieverts in a year. No
averaging because that is what you are going todesign against, that is what you are going tomonitor against. And of course we maintain theorgan restrictions which are not sufficiently
protected by the effective dose. So this isstability in the system, it means that perhaps
Basic Safety Standards from the international agencies do not need to be revised because the limits
are the same, they can be complemented or supplemented with the development of advise on theconstraints which are identified in the Basic Safety Standards but not developed. So ourrecommendations can clearly be seen as an evolution, to build from the Basic Safety Standards.
So now I turn to optimisation. Having ensured that no individual is exposed to undue risk from asource, there is a duty to do better and it is the responsibility of operators and national authorities. It
is not the duty of ICRP. ICRP can advise on how it might be undertaken optimisation is a national
issue. The level of protection which you aim to achieve in Japan is a Japanese issue and it will be9different for nuclear power, for hospitals, for awaste repository, for individual applications.
You will optimise protection in all thosesituations for workers and for the public andyou come up with authorised levels for
operation. And your levels will be different to
the levels in the UK, at which operation is
authorised by the regulator, different to thefigures that the French will authorise, and all
will be very different to the level which the US
authorises. But optimisation is a national issue and we believe that we are best advising the world in
optimisation if we advocate of basic safety culture which is defined in the Basic Safety Standards. It
requires cooperation between all of those
involved and tomorrow you will about this inmuch more detail. The Basic Safety Standardsof the NEA and the other international agencies
define safety culture as the assembly of
characteristics and attitudes which establishes
that, as an overriding priority, protection andsafety issues receive the appropriate attention.
So, it is the idea; the idea, the noun, English
noun, my thinking, that is what I amemphasising, optimisation is about thinking, it
is not mathematics.
So we are recommending to you all and you will spend tomorrow looking at stakeholder
involvement involving those who are actually
exposed. It may be very challenging for the
regulator, to have to engage with the public, toempower the workforce, but this is the job of
the national authorities and the operators
together, to get the best level of protection in
the circumstances.
Now for the protection of groups we have torecognise that in the past collective dose has
been defined as the double integral, but it isdifficult to use because it aggregates, it brings together, a vast amount of information into a single
number which can then be misused. So what we think is needed for decision-aiding is the dose
matrix, I will leave the rest to you John. We want to see individual doses when they are received. It is
important when you make a decision to know whether the dose is going to be received 1000 years
10from now, in the year 3000, or whether it isgoing to be received tomorrow. And it wasargued to me that for the workforce collective
dose is useful but I would disagree with that, I
think you need at least the number of workers
involved, it is no use just to say the collective
dose has been reduced if you have many moreworkers exposed. Or even the other extreme,
only one or two workers are receiving the entire
dose. That may not be the optimised protection.
So you will discuss this more tomorrow.
I move on to Exclusion. ICRP is recommending levels of activity concentrations below which
effectively you do not treat the materials as radioactive. For artificial radionuclides these are below
0.01 Bq per gram for alpha or 0.1 Bq per gram for beta gamma emitters. For the naturalradionuclides, we recommend activity concentrations of 1 or 10 Bq per gram for potassium 40. Thishas been a difficult issue for international agencies for many years. Which level of activity in a
foodstuff should not demand intervention by
the regulator? And, clearly, we have had
exemption levels, regulators use exemptions, it
is a valuable tool. But an exemption is nodifferent really from an authorisation todischarge; the regulator loses control of theradioactive material. But there will still be someconsiderations of the system of protection.
What we have done is look at where exemption
levels have been devised in different
circumstances and decided that at these sets of activity concentrations nobody has gone lower thanthis, essentially to exempt. So let us treat these as levels below which you regard the materials as notradioactive.
Protection of the patient, as I come towards
the end of my presentation, is different, as I
have said, here I will not speak very extensively
on this today, but justification is somewhat
different in the case of patients because you aredeliberately irradiating the patient and in asense you are doing it for the benefit of thepatient, you are going to diagnose somethingwhich will increase the probability of good
health in the patient. So firstly you have to11

ensure that the general procedure is okay. So the regulator is going to say that PET scans are justified
generically and there are some things which you may decide are not generically justified. But you
may decide PET scans are a good thing. Then when a patient presents with symptoms, you are goingto refer that patient for a diagnostic X-ray or some diagnostic technique. The referring physician has
a job of justifying why that patient needs the exposure that it has to be a CT rather than a simple
chest X-ray, why it has to be a combination of CT and PET. No problem, as long as it is justified thatthe benefit to the patient is greater than the detriment from the exposure, the dose that the patient
receives. Which is exactly as it ought to be, because if you find the early stages of a tumor or someother problem that will reduce the life expectancy of the patient, then the doses were justified – youare going to improve the health of the patient? What is not justified is routinely giving a CT to every
member of the public every year just in case they might have a cancer. I would say that is notjustified. Optimisation of the procedure should be undertaken, and we believe that diagnostic
reference levels as indicated in good practice are an aid to optimisation. And you need the constraints,
the maximum doses that you are going to allow for comforters and carers. And the actual doses thatare applied may be different, in different countries, because of different social situations, and it is amatter for the regulatory authority and for the medical people, ICRP can give generic guidance.
Potential exposures, we also deal with those
events which have a probability but not acertainty of occurring and here we turn our dose
constraints into risk constraints, we say you
have to be careful about using effective dose,and here you can see the figure of a 100 millisieverts again that we have decided is about as
far as you can go in using effective dose,
because above that individual organ doses may
be sufficiently high that there can be tissue
reactions. What we used to call deterministic
effects here, tissue reactions. And for events that may affect large numbers of people of course, there
can be a range of consequences, early effects of tissue reactions, late effects, such as cancer, you can
get contamination of the ground, you can get
economic losses by contaminating factories’
property, it can multi-attribute a situation which
no-one has managed to resolve by use of asingle quantity and therefore we think you haveto restrict the probability of the event occurring.
Protection of the environment you know
about because ICRP decided at the end of lastyear to establish its fifth standing committee todevelop a policy and a framework for12environmental radiation protection. Committee 5 will be establishing the reference and environment
which you will know about from Publication 91 and you will also know that one of the reference
fauna is a duck, so here is my duck, this is one of the standard reference fauna and I think thatreference flora involve things like seaweed, but I thought this lily was rather prettier for my reference
flora.

So, I end, Chairman. As you know, we havereleased the text in the last month - it is on the
web – the supporting documents, thefoundation documents are courtesy ofCommittees 1, 2, and 4, which meet courtesy ofProf. Pan, in Beijing in October to finalize thesupporting documents and we will consider, asa main commission, early next year all thecomments that we get back from the web.
Thank you for your attention.

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