|Main comments regarding the 2005 draft recommendations of ICRP from the ad hoc working group set up by the French Society for Radiation Protection
The working group set up by the French Society for Radiation Protection to study the ICRP proposals consists of about thirty members representing the stakeholders in radiation protection in France: authorities, experts and professionals from the nuclear, medical and research fields, as well as representative of non-governmental organization.
The working group met twice to comment the RP05 document. Due to the short time available, it was not possible for the working group to enter into the very details of the paragraphs' wording for the whole document. As a general rule, the working group notices that these new recommendations present an evolution of the ICRP 60 radiation protection system, with a notable evolution of some concepts, particularly that of dose constraint, which would merit more explanations in order to improve their understanding.
The working group endeavored to formulate its comments on the topics he considered as essentials. Four topics have been addressed:
- The dose constraint
- The medical field
- The exclusion
- The dosimetric quantities and units
This document states the main conclusions reached by the working group. It is intended to reflect the various opinions expressed during the working sessions.
2. The dose constraint
The 2005 recommendations propose 4 values of source related individual dose constraints applying whatever the exposure situation (normal, existing, or emergencies). The multi-source individual dose limits for the workers and the public are maintained for normal exposure situations.
The working group notices that the concept of dose constraint becomes a powerful tool in the radiation protection system. This concept appears to be very useful for radiation protection of the public, where it brings some flexibility, notably for the management of installations discharges. As far as the occupational radiation protection is concerned, the majority of the working group members considers that this tool should be mainly used by operators, within the framework of optimisation of radiation protection, and more particularly to establish dose constraints per operation. The majority of the working group considers that it would be desirable that constraints per source for occupational exposure do not become regulatory values and values which can lead to a statutory offence if they are exceeded.
In all cases, the definition of "the source" related to any constraint must be defined in consultation with the concerned players.
The working group notices a contradiction between §132 which specifies that the respect for constraints represents a level of protection which should be considered as obligatory ("They provide a level of protection that should be considered as obligatory and not maintaining these levels of protection should be regarded as a failure") and §137 which notices that constraints may be used as a regulatory tool ("Although it may be used as a regulatory tool, so that exceeding a mandatory constraint may be a statutory offence,…"). The ICRP should be more precise on the regulatory nature of constraints, and notably on the meaning of "failure" (§132) and "statutory offence" (§137).
In this spirit, the working group proposes a new wording of §137:
§ 137 "(...) Although it may be used as a regulatory tool, which in specific circumstances may give rise to a statutory offence when the constraint is exceeded, it will not cause a step change in the associated health risk".
Some members of the working group consider that the mention, in §164 – 3rd bullet, of a dose constraint equal to 0.3 mSv/year for public exposure in normal situation is too restrictive and can lead to confusion given that the value of 1 mSv/year is proposed in a generic way. If such a value of 0.3 mSv/year had to be proposed by ICRP, more explanations should be provided.
3. The medical field
The members of the working group consider that, as a general rule, further efforts remain to be made to continue to foster a culture of optimisation of radiation protection among radiology practitioners. They wish that the necessity to pursue the efforts were explicitly mentioned in the RP05 which, in its current state, does not give sufficiently strong messages regarding this subject.
A majority of the working group members considers that the §116 mentioning the risk associated with the exposure of pregnant women should be modified. While making reference to ICRP 84 and ICRP 90 data, in which a threshold for malformation effects was situated at 100 – 200 mGy or higher (cf ICRP 84: "malformations have a threshold of 100 – 200 mGy or higher"), the current formulation of this paragraph does not propose a numerical value. It says that from animal experimentations, it exists a true dose-threshold of 100 mGy and that the Commission judges that risks of malformation can be discounted for doses "in the range up to a few tens of mGy". In order to allow the management of in utero exposures and to be coherent with the previous ICRP publications, it would be preferable to clearly indicate the value of 100 mGy as the threshold-dose for human malformations.
The §116 should be formulated like this: "In respect of the induction of malformations, the data strengthen the views that there are gestation age-dependant patterns of in utero radiosensitivity with maximum sensitivity being expressed during the period of major organogenesis. Malformations have a threshold of 100-200 mGy or higher; therefore for practical purposes, the Commission judges that risks of malformation after in utero exposure to doses up to 100 mGy may be discounted."
Regarding the justification of a procedure for an individual patient (§219), the working group considers that it would be appropriate for the ICRP to specify that justification of the choice of a diagnosis technique must make allowance for the availability of equipment and for economic and social constraints.
The §222 specifies that "The medical procedures causing patient exposures are clearly justified". Some members of the working group consider that it should be added that the procedures are justified "provided that codes of good practices have been established".
4. The exclusion
The ICRP recommends generic exclusion levels expressed in terms of activity concentration of radionuclides in Bq/g.
The values proposed by the ICRP are disputed by several members of the working group who consider that, in some situations, the ingestion over long term periods of foods containing nuclide concentrations equal to the exclusion values would lead to individual doses of several mSv, which would in their eyes be unacceptable.
The formulation of §206 ("The Commission has concluded that these values provide a practical definition of what is to be considered radioactive ...") makes think that the exclusion values define the border between what is radioactive and what is not radioactive, which is also unacceptable for some members of the working group, and anyway, inexact according to physics.
Moreover, some members of the working group consider that the exclusion of radioactive materials should not be decided in a generic way. It is necessary to adopt a management on a case by case basis, with a control of the recycling process. Other members estimate that, without searching for a trivialization of situations presenting artificial radioactivity, it would be useful to adopt exclusion values, notably for the dismantling of installations. Instead of an approach using generic exclusion values in terms of activity concentration, some members of the working group suggest to adopt a value in terms of dose (for example 10 µSv/year) and to perform studies on a case by case basis.
5. The dosimetric quantities and units
Some members of the working group appreciate the revision of weighting factors for neutrons proposed by the ICRP (§ 68 to 74). This revision allows to comply with the physics laws while not modifying considerably the representativeness of operational quantities as estimates of effective dose.
The working group considers that the replacement of the equivalent dose by the "radiation weighted dose" (§51) is a good thing, but that the J.kg-1 unit is inappropriate. The working group maintains its suggestion to use the Weighted Gray, designated Dw. This would allow to avoid the introduction of a new unit to replace the Sv of the equivalent dose.
Some members of the working group wish that the ICRP reminds the domain of validity of weighting factors used for the calculation of the effective dose, as it was the case in ICRP 26.
In the section dedicated to the definition of absorbed dose (3.3.1), some members of the working group consider that the first sentence of §46 (" For densely ionising radiation (charged particles from neutrons and alpha particles) and low doses of low LET radiation, the frequency of events in most cells is zero, in a few it is one and extremely exceptionally more than one.") is ambiguous and would deserve a new formulation.
The French Society for Radiation Protection would like to thank the ICRP for having initiated a consultation for the RP05 document. As a general rule, the majority of the working group appreciates the new formulation of the recommendations and notably the fact that the comments proposed to ICRP during the previous consultations have been taken into account. However, further efforts remain to be made to better clarify the concepts and their use.