2005 ICRP Recommendation

Draft document: 2005 ICRP Recommendation
Submitted by Ted Lazo: Comment 2 of 5, OECD Nuclear Energy Agency (NEA)
Commenting on behalf of the organisation

NEA Comments on Specific Paragraphs: (submission 2 of 5) (13) The primary aim of the Commission is to contribute to the establishment and application of an appropriate level of protection for (inserted: human individuals) (Comment: The ICRP recommendations are to protect individuals as well as "the human population" as a whole. It is thus suggested to more specifically state this while maintaining the idea of broad protection of all humans.) (Deleted: the human population) and, where necessary, for other species without unduly limiting the desirable human actions and lifestyles that give rise to, or increase, radiation exposures. (16) The term ‘source’ is used by the Commission to indicate the cause of an exposure, not necessarily a physical source of radiation. For example, when radioactive materials are released to the environment as waste, both the installation as a whole and the discharged material can be regarded as sources, depending on the context. The term ‘exposure’ is used by the Commission to mean the process of being exposed to radiation or radioactive material. Exposure (added s) can then lead to (Insert: a whole- or partial-body dose to) (Comment: This wording of this last sentence was a little confusing, it seems to refer to the possibility of partial body exposure. If this is what the Commission intended, the new text is felt to be more clear) (Deleted: a dose to some part of) the exposed individual. (18) (Insert: Justification in the context of radiological protection involves the broad, judgemental) (comment: There is a need here for introductory words as to what justification IS, in addition to who is responsible as described in this paragraph. It would also be very helpful if ICRP described the elements of Justification decisions, while clearly not making justification decisions. Don’t forget Justification as a part of how to address actions in Existing and Accident situations, which must also be justified. The proposed phrase is provided as an example, not necessarily as final text.) (Insert: decision as to whether or not performing or allowing an action will do more good than harm. Other than medical exposures, this refers to decisions regarding proposed or ongoing licensed activities in normal situations, and to decisions regarding the implementation of specific protective actions in emergency or existing situations. For example,) judgements on whether it would be justifiable to introduce or continue a particular practice involving exposure to ionising radiation are important. Alternatives to existing practices may develop over time, which would require that those practices that do exist should be periodically re-examined to ensure that they are still justified. Justification is (insert: thus a necessary prerequisite or first step for any decision regarding radiological protection actions or approvals.). (Comment: It is important that the Commission state that Justification is necessary, but then should go on to discuss the responsibility for justification) (Deletion important anym wn such decision can b made)The responsibility for judging the justification of a practice usually falls on governments or government agencies, (insert: or other relevant parties,) (Comment: So as not to be ONLY the responsibility of government) to ensure an overall benefit in the broadest sense to society and thus not to each individual (Comment: The reason for this caveat is not clear, need to be more clear with this ore delete it.) Governments make these decisions for strategic, economic, defence and other reasons and radiological protection considerations are recognised as being (Comment: The objective of this paragraph should be to put radiation protection input into perspective, not to diminish its importance.) (Deleted only) one input that could influence the justification decisions. (Deleted: Therefore, while justification is a prerequisite of the complete system of radiological protection, the methods of ensuring justification are largely outside the scope of these recommendations) (insert: Radiation Protection has its role in the complex process or justification, and should be considered as one factor or element. In this assessment, comparison with other practices and/or remedial actions that have already been justified can be useful.) (Comment: The Group felt that Justification is NOT outside of the scope of these recommendations, but the radiation protection aspect of the justification process needs to be seen in its proper perspective.) (20) It is implicit in the concept of a practice that the radiation sources that it introduces or maintains can be controlled directly by action on the source. The Commission then aims to apply its system of protection to practices that have been declared justified. However, the system may also be applied in situations where the practice has not been declared justified. (comment: It is not clear to what this sentence refers. This should be deleted or clarified. A specific example of such a situation might help.) (24) There are many sources for which the resulting levels of annual effective dose are very low, or for which the combination of dose and difficulty of applying control are such that the Commission considers that the sources can legitimately be excluded (Comment: Should controllable sources, low dose or not, be excluded? The EGIR felt that the text in the IAEA report on Exclusion was more correctly nuanced in this area, and should be considered by the Commission for its description of Exclusion.) completely from the scope of its Recommendations. Since all materials are radioactive to a greater or lesser degree, the concept of exclusion is essential for the successful application of the system of protection. In principle, it can be applied to both natural and artificial sources of radiation although in practice it will largely be of use in the control of natural sources. The Commission considers that numerical criteria for exclusion would assist in the consistent application of the concept. Its recommendations are found in Chapter 8. (25) Sources and exposures that are not excluded are within the scope of the system of protection. These sources and exposures should be subject to appropriate authorization by the relevant regulatory agency. (Comment: The EGIR felt that the last sentences of paragraph 25 were somewhat redundant with paragraph 26. The suggestion thus puts these two paragraphs together. The concept of a graded approach to regulation, from the deleted section of paragraph 25, is, however added elsewhere to the new paragraph 25) .(Deleted: The commission recognizes that there are also circumstances where sources are within the scope of the Recommendations, but where regulatory provisions maybe unnecessary because additional protective actions are not needed. In such cases exemption may be granted through a regulatory decision (26).) In order to avoid excessive regulatory procedures, (insert: a graded approach should be taken to regulation, and in situations where further regulatory controls add little or no additional protection) provisions can be made for granting exemptions (Deleted: in cases where it is clear that further controls are unnecessary). The regulatory act of assessing the situation and granting an exemption is, in itself, a form of authorization (Comment: The term Authorisation seems to be used here is generic form, as in the upcoming NEA report attached here in annex. Because the term Authorisation is used in some national regulations in a much more restrictive form, this could perhaps be explained briefly here, with reference to the NEA report.) and the material that is exempted remains subject to the system of protection, although without further regulatory control. (28) The practical application of the concept requires derivation of (insert: radiological criteria to be considered when assessing whether authorisation should be granted for a source or exposure situation to be exempted. Several aspects should be taken into account, such as the nature of the activity or source, the total activity to be exempted, the expected exposures and exposure distributions, and the costs and benefits of possible regulatory controls.) (Comment: The EGIR feels that there are many aspects that should be considered when granting an exemption. The additional text attempts to outline some of the key aspects that the Group feels are important.) (insert: For this purpose, )exemption levels in terms of activity concentration, (insert: have been developed and agreed to internationally). These levels should enable exemption of appropriate sources of exposure including wastes containing very low levels of activity. International agreement on a single set of radionuclide-specific levels for exemption would facilitate a consistent regulatory approach worldwide. Sources with activity concentration above exemption levels need not necessarily be subject to the full rigour of regulations. A graded approach to regulation based on assessed hazard would focus regulatory effort onto areas where most benefit would be obtained. (31) Several features influence the ways in which the Commission’s aims can be implemented. These include the nature and magnitude of the health effects due to exposures to radiation and the form of dosimetric quantities used to specify unequivocally any quantitative recommendations. The inevitable and ubiquitous exposures due to natural sources are also important. The existence of this natural background of radiation means that, in practice, the radiation risk factors required for use in protection are those applicable to increments of, or additions to, doses above 1 or 2 millisieverts in a year. This is because an absolute dose of 0.01 mSv cannot be received in isolation, but rather an additional 0.01 mSv above the natural background and it is the incremental risk of the exposure that is of interest for decision making. These features are discussed in Chapter 5, which sets out the Commission’s general system of protection.(Comments: It is not clear what this paragraph adds in terms of explaining format of the recommendations. It is suggested that this paragraph be deleted, or altered to express useful information.) (38) Radiological protection in the low dose range is primarily concerned with protection against radiation-induced cancer and hereditary disease. These diseases are termed stochastic effects, as they are probabilistic in nature and are believed to have their origins in damage in single cells. For protection purposes, it is assumed that these effects increase with increasing radiation dose, with no threshold, and that any increment of exposure above the natural background produces a linear increment of risk. (Comments: The EGIR feels that this last phrase "above natural background" in this context warrants much more explanation, particularly in that earlier in the document the fluxuation in natural background is mentioned. Similar clarification is needed in paragraphs 160 and 161.) (40) At higher doses, associated mainly with accident situations, tissue reactions (Comments: As mentioned in the comments on terminology, the EGIR suggests that the Commission contiue to use the term Deterministic Effects) formally called deterministic effects) including acute effects, and late effects such as cataracts of the lens of the eye, necrotic and fibrotic reactions in many tissues and organs, may occur if exposures exceed a threshold dose. This threshold varies with the dose rate, especially for exposures to low LET radiation. High LET radiation, from neutrons and alpha particles, causes more damage per unit of absorbed energy than low LET radiation. Values of Relative Biological Effectiveness (RBE) for tissue reactions for high-LET compared with low-LET radiations have been determined for different biological endpoints and different tissues or organs. In general the RBE values were found to be smaller than those for stochastic effects and to vary with the tissue damage described. The application of values of the radiation weighting factor, wR, for assessing the tissue damage from high LET radiations would, therefore, result in an overestimate of the likely occurrence and severity of any tissue damage. When assessing radiation exposure for determining the potential for tissue damage, the average absorbed dose, weighted by an appropriate value of RBE for the biological end point of concern, should be used (see Section 3.6). (45) At a given absorbed dose, the actual value of energy imparted in a cell (the elementary unit of life) is given by the product of frequency of energy deposition events and the value of energy deposited in each event. At a given (low) absorbed dose, for less densely ionising radiations (photons, electrons) the energy imparted in each event is low and more cells experience energy deposition events than in the case of exposure by densely ionising radiation. As a consequence, also the fluctuation in the energy imparted among cells is therefore smaller (Comment This paragraph is very difficult to understand, and the significance of its message - that low LET radiation deposits energy more evenly than high - is unclear. This paragraph should be rewritten to be more clear.) (46) For densely ionising radiation (charged particles from neutrons and alpha-particles) (Comment: These examples of densly ionising radiation are somewhat unclear - does this refer to secondary charged particles from neutron and alpha collisions? This should be clarified) 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. The value of energy imparted in most individual cells is then zero but in the hit cells it will exceed the mean value by orders of magnitude. These large differences in the energy deposition distribution in microscopic regions for different types (and energies) of radiation have been related to observed differences in biological effectiveness or radiation quality. (54) It must be stressed that effective dose is intended for use as a principal protection quantity for establishment of prospective radiation protection guidance. It should not be used to assess risks of stochastic effects in retrospective situations for exposures in identified individuals, nor should it be used in epidemiological evaluations of human exposure, because the Commission has made judgements on radiation risks in the derivation of ‘detriment’ for the purpose of defining tissue weighting factors. Its main use is to enable external and internal irradiation, (insert: as well as non-uniform irradiations,) (comment: This has been added to cover all situations appropriately) to be added as a means to demonstrate compliance with the Commission’s quantitative restrictions on dose, which are expressed in effective dose. In this sense effective dose is used for regulatory purposes worldwide. (55) Effective dose is defined by doses in the human body and is in principle as well as in practice a non-measurable quantity (Comment: Note that most other dosimetric quantities, at the same level as effective dose, can not be measured. So why stress such a fact here?). For estimating values of effective dose, conversion coefficients are generally applied which relate the effective dose of a person to other measurable quantities, e.g. air kerma or particle fluence in case of external exposure or activity concentrations etc. in case of internal exposure. In order to provide a practicable approach to the assessment of effective dose, in particular for occupational exposure to low doses, conversion coefficients are calculated for standard conditions (monoenergetic radiations, standard irradiation geometries, selected chemical compounds) in anthropomorphic phantoms with clearly defined geometry, including all organs specified in the definition of effective dose and all regions (including surfaces of bone mineral and airways, contents of walled organs, and volume of organs) where radionuclides might reside in the body. 3.4.1 Radiation weighting factors (Comment: The modification of weighting factors, as described in this section, is well supported and scientifically well expressed. However, this section, in general, is too detailed and should be shortened, with the details put into an annex or a separate foundation document) (67) While there are good arguments for continuing to keep wR for low-LET radiations equal to 1, it is important to state that this simplification is sufficient only for the intended applications of the quantity effective dose, e.g. for dose limitation, assessment, and controlling of doses, but not for the retrospective assessment of individual risks of stochastic effects from radiation exposures or for use in epidemiological evaluations. In those cases, more detailed information on appropriate RBE values should be considered.(Comment: Perhaps you should reference paragraphs 36 and 66, or add other text, to give examples of those cases where 1 would not be the appropriate value.) (82) (insert: As addressed in section 2,) radiological protection is concerned with controlling (Comment Does controlling in this context include preventing exposures? If not, perhaps "or preventing" should be added here.) exposures to low radiation doses that give rise to stochastic effects, and preventing exposures that could give rise to high radiation doses resulting in tissue damage (deterministic effects). (insert :For practical reasons,) these two types of effect are considered separately below. (Comment: This section is not the place to specifically define the aims of radiation protection - this was done broadly in section 2. However, presenting these goals here as a vehicle for discussing different practical approaches to the control of stochastic and deterministic effects seems more appropriate. Otherwise, perhaps these RP goals should be clearly expressed in section 2.) (84) The definitions of the operational quantities take account of the common situation in which the individual dose assessment is performed with dosemeters worn on the body. The personal dose equivalent is, therefore, defined by the dose at a specific depth in the body below the point where the dosemeter is worn. The protection quantity adopted by ICRP for the control of stochastic effects is the effective dose. This quantity is by its definition related to doses in the human body and generally is not measurable. (Comment: This was already noted in paragraph 55, but does not seem to add much in this paragraph. It is suggested to delete this sentence.) A variety of conversion coefficients link the effective dose to measurable physical quantities, e.g. radiation fluences or air kerma characterising the external radiation fields in the workplace.