|STUK comments, Part 2 of 2
2 Detailed remarks
2.1 Effective dose (see our principal remark 1.6 above)
(i): The generic definition of the effective dose allows one to estimate the effective dose by using reasonable estimates of the doses to the organs of the person(s) being exposed to ra-diation. We hope that ICRP will give some supplemental information on how to proceed, when the exposed group consists of just one gender, or is an individual of either sex, and therefore does not have all the organs that are shown in the tissue weighting factor list. One could define effective dose to always be used in relationship with hermaphrodite human models with all the organs (or in relationship with separate male and female phantoms and taking the doses to sex-dependent organs from these), but this is not self-evident without saying and is not always reasonable. Another interpretation could be to use just the male or-gans for males and female organs for females. Of course, these two possible interpretations lead to different results if the same set of weighting factors is used in both cases. Therefore, we suggest that the Commission considers giving gender-specific weighting factors, or at least would give explicit advice on how to deal with the gender-specific organs in various situations.
(ii): At least in principle, the organ doses should be estimated according to the size of the person(s) exposed: child phantoms should be used for children and adult phantom(s) for adults, and ideally even matching the person’s actual size. The acceptability of this can be inferred from item 88, which suggests that “individual specific characteristics” should some-times be taken into account, and item S15 suggests that any model for the human body may be used as long as the dosimetric model is specified or implied. The matter needs further clarification, however.
(iii): If the organ dose determination must be done as an average over a wide distribution of ages and both genders, unambiguous calculation of the effective dose will not be possible in a situation where the radiation field is not sufficiently uniform – there is no way of placing the different-sized phantoms in an unambiguous way with respect to the radiation field.
(iv): ICRP uses the same name and symbol for effective doses calculated with different sets of tissue weighting factors. In the future, this is likely to add confusion to the use of the quantity – differences between the effective doses calculated by using different tissue weighting factors may be considerable in some cases. Is it possible, for example, to denote the weight set used by some kind of an index, or another qualifier?
(v): The collective effective dose is mentioned in item 198 with a reference to Publication 60, but the unit of this quantity is not declared. Should it be mansievert, personsievert, or something else? It is very important to clearly distinguish the collective dose from the mean dose. Further, what would be the unit of the collective radiation weighted dose in a specified organ (collective equivalent dose in ICRP 60)?
(vi): Item A42 requires that the mass-averaged gonad dose is used. This is a new interpreta-tion. Why are the testes given more than three times the weighting of the ovaries? One could expect that the risk of inducing genetic harm would depend more on the dose than on the energy absorbed in the organs. Most often so far, the arithmetic average of the two organs has been used for gonad dose, and ICRP 71 specified that in the calculation, gonad dose is taken to be the larger value of the dose to testes and the dose to ovaries.
2.2 Chapter 4.2 The induction of cancer and hereditary effects
The Dose and dose-rate effectiveness factor (DDREF) of 2, as in ICRP 60, is not well founded (rather a dose-rate effectiveness factor (DREF) for low dose rate only). New data from the Life Span Study does not support any reduction factor for solid tumours for acute doses less than 0,2 Sv. So, even though in item 6 it is noted that “new scientific data have been produced since 1990”, this new data is not fully reflected in the draft. For calculating new tissue weighting factors this is not of great importance (only the weight of red bone marrow would be reduced in relation to other tissues), but for expression of the total detriment (table 6) it is crucial.
The numerical value of the total nominal detriment is actually not of much use for professional deci-sion makers. For educational purposes, the coefficient for cancer mortality is more important and will still be used, as it is easier to explain. The simple factor, 5% per mansievert, without undue exact-ness, is well known and should not be reduced without good reason. For policy reasons, a reduction to 4.4% should be avoided. It gives a false impression of exactness without being based on solid new data.
2.3 Chapter 7.2. Distribution of exposures in time and space
There is no need to go further than ICRP 60, which stated in item 35: “If the ranges of individual dose or time are large, it may be useful to subdivide the collective quantities into blocks covering more limited ranges of dose and time”, and in A35: “The time period and population over which the collective dose is summed or integrated should be specified”. These statements are still valid and may be repeated as such. But the recommendation in item 201 to adapt a “dose matrix”, the compo-nents of which can be further weighed according to the values and preferences of those involved in the decision, opens a very questionable path to arbitrariness. This does not seem ethically defendable.
The defence of a move from a utilitarian approach to a more individual one (item 6) disregards the fact that ICRP 60 offers good protection for both the individual and the group.
2.4 Chapter 11. The Protection of the Environment and Annex B. The protection of Non-Human Environmental Species
STUK welcomes the introduction of the protection of non-human environmental species in the work of the Commission and the establishment of Committee 5 to develop the approach of protection. The methodology presented in the current draft recommendations is in line with the work being carried out by other bodies, such as IAEA, UNSCEAR and EC.
2.5 Summary of the Recommendations: Exclusion of radiation sources item (S12),
Section 2.3.: Exclusion and authorization of exposures, and
Chapter 8.: Exclusion of sources from the scope of the recommendations
The titles of these Chapters and Sections are confusing and the contents of them are to some degree contradictory. The benefits of the current proposal, which involves mixing internationally accepted and widely-used concepts, exclusion (of exposures) and exemption or authorization (of practices and sources within practices), together should be reconsidered once again. If the term exclusion would be accepted to be used as proposed, the exercise of trying to deal with artificial and natural radiation together has made Chapter 8 very unclear.
As a minimum amendment, Tables S2 and 10 should be divided into two separate tables, because the basis for “exclusion” in cases of artificial and natural radionuclides differs from each other; in the first case it is the triviality of resulting doses (exemption) and in the second case it is the recognition that most material contains natural radioactivity and that control is impractical (exclusion). The ex-clusion activity concentrations for natural radionuclides are, as recognized, agreed internationally and published in the IAEA Safety Guide RS-G-1.7.
Regarding artificial radionuclides, the effort of defining what is not radioactive (due to trivial expo-sure) cannot be completed yet, because the Codex Alimentarius is not yet published. Furthermore, the lowest number for á-emitting nuclides in the IAEA Safety Guide RS-G-1.7 is 0.1 Bq g-1 and not 0.01 Bq g-1.
As a matter of fact, the abovementioned documents are sufficient and numerical “exclusion” levels for artificial radionuclides are not needed in the ICRP recommendations. Moreover, the requirements of ICRP 60, that the practice candidate for exemption has to be justified and inherently safe, are missing here. Accordingly, all kind of frivolous sources would be excluded, if the radionuclide con-centration is below the limits given in Tables S2 and 10.
2.6 Table S1. and table 7.
The tables are problematic. The lowest number, 0.01 mSv in a year, should be deleted due to the clear discrepancy of concepts in the tables (maximum constraint versus minimum value of any con-straint). The latter message can be given in the text as it is in Chapter 8, Item 205.
It is also somehow striking to call 1 mSv in a year a maximum constraint from a single source when the effective dose limit of 1 mSv in a year still remains valid.
The text column related to 100 and 20 mSv in a year, annual continuous exposures, and short time exposures in emergency situations for workers or sheltering, for example, are mixed together in a confusing way.
The example of 20 mSv as an appropriate intervention level for stable iodine is extremely high, as it translates into a thyroid dose of 400 mGy. Most of the Belarussian children with thyroid cancer after Chernobyl had received less than 300 mGy to the thyroid. The intervention level for stable iodine should be given as organ dose and not as effective dose. The table, and the corresponding text in item 164, is not the right place for this type of recommendation. The intervention levels for emergency should be taken out of this context. The broadening of the term “constraint” to cover intervention levels appears artificial and opens the possibility of misunderstanding.
The proposed new term radiation weighted dose is good, clear and simple. It is especially important to stop using sievert for tissue or organ dose. This use has caused serious misunderstandings, when a modest effective dose has been interpreted as a modest local dose and the danger of local determinis-tic effects has been overlooked.
2.7 Chapter 4.2.4. Radiation effects in the embryo and fetus
Item 118: This paragraph states that exposure in utero should not be a specific protection case ….where the prolonged dose is well below approximately 100 mSv. Because of the recognised in-crease in risk of childhood cancer after exposure in utero, estimated as 6% per Sv, this should be more stringent, “below 10 mSv”, for example. For a dose of 40 mSv, any case of childhood cancer would have a 50% probability of being caused by the exposure. This argument should be enough to protect the fetus from such doses, even though the risk may be lower for prolonged exposure.
2.8 Chapter 6.5.2 Limits for individual organs or tissues
Item 186 and table 9: The unit Sv should be replaced by a unit for radiation weighted dose.
2.9 ANNEX A
Explain the dose quantity used in Table A.1. The reference to a unit (Sv) is not sufficient. (Radiation weighted dose in the organ considered?)
Item A17: The notation “X cases per 10,000 people/Sv” is confusing. If written in words, it should rather read “X cases per 10 000 people and per Sv”. This is again an example where ”manSv” could be used. It is important to distinguish the expression X/(10 000 people ∙Sv) from X/(10 000 people /Sv).
(Also, according to SI guidance on notation of numeric values: 10,000 = 10.000 = 10 while 10 000 = 10000 = 104).
In Table A.1 the unit “cases per 10,000 PYSv” is not correct: it should not include “year”. Also, in relationship with units, P reads “peta” (= 1015). In fact, “cases per 10 000 manSv” has been intended. If the concept of collective dose is used, perhaps “cases per 10 000 persons and per Sv” or just prob-abilities per Sv could be used. However, if a new unit for radiation weighted dose is introduced, it should replace the Sv in this table.
Item A42: The dose to the colon as the mass-weighted mean of ULI and LLI doses was not defined in Publication 60, where ULI was included in the remainder tissues. This definition has been intro-duced in later publications.
3. Editorial and other comments
It is not mentioned that the recommendations concern ionising radiation. It should be mentioned in the summary and in the introduction.
Add the word probability (or likelihood) in item 38: “it is assumed that the probability of these ef-fects increases with increasing radiation dose”.
Several special characters (sigma, gamma, alpha, and so on) have not been printed correctly.
Item 140, the 2nd sentence is not clear. Should perhaps be: The operator is responsible for providing input to the optimisation that will be established by the authority for…
In item 146, it is unusual to see “exposures of the staff” as a type of exposure falling under “medical exposure”. Probably this is not the intention? The ICRP should rephrase this paragraph so as to avoid any possibility for such a misinterpretation. Exposure of the staff belongs to the occupational expo-sures.