7. ICRP Draft Section 4 - Biological aspects of radiological protection
It is noted that probability coefficients for radiation detriment are now calculated by a different method and have in general dropped in magnitude from ICRP 60 values. Perhaps it is puzzling that while these values have in the main reduced (albeit moderately) equally, or in some cases, more stringent protection measures etc are being put forward. Some will object to this. However, NRPB staff would not support any move to increase exposures on these grounds. The modest changes would not justify relaxation of protection measures. Care is needed in presentation.
Risk estimates for radiation-induced cancer are based solely on the A-bomb Life Span Study (LSS). Mention of other studies is cursory in the main text and annex. It would be helpful to have a little more discussion of other data, particularly radon-induced lung cancer and Thorotrast alpha-induced liver cancer for which there are good data, because comparisons with LSS risk estimates provide support for approaches taken to alpha dosimetry.
Table 5 gives detailed technical comments on Section 4 of the draft ICRP 2005 recommendations.
TABLE 5 Technical comments on biological aspects of radiological protection
97-99 Perhaps this section on the induction of tissue reactions should refer to/justify the dose limits given in Table 9 for individual organs/tissues.
98 It would be helpful to have a clearer distinction/explanation of differences between generic and consequential late reactions.
100/101 Would it be better to use mGy rather than mSv? Basic judgements on cancer risk are being considered, including the account to be taken of RBEs and dose rates and cellular responses.
108 The factor of 5 reduction in the estimate of genetic risks compared to ICRP 60 is substantial but receives little comment from ICRP. It would be useful to include in Chapter 9 a comment on whether this reduced risk estimate should have any influence on the use of gonad shields in diagnostic radiology.
109 The exclusion of minisatellite data is sound at present. There is a slight confusion/inconsistency with a statement in Annex A that most radiation-induced hereditary mutations are large multi locus deletions. The minisatellite data are probably sufficient to question this.
111 Does it need to be more specifically stated that the figures are based on incidence - it is not until Annex A that it becomes really clear that most emphasis is now on incidence rather than mortality?
6.2 10-2 Sv-1 should be 6.4 10-2 Sv-1 according to Annex A.
4.8 10-2 Sv-1 should be 4.9 10-2 Sv-1 according to Annex A.
Table 6 See comment above does this explain the possible rounding error as the whole population cancer risk is 6.2, the heritable effects is 0.2 but the detriment is 6.5 rather than 6.4?
Table 6 of Chapter 4 uses values from Table A1a and A1b in Annex A, but the column title is slightly different. What is the nominal probability coefficient? Is it the same as the nominal risk coefficient?
It is interesting that the evidence is that the value of detriment has been reduced from ICRP 60 and yet the emphasis of these recommendations seems to be to further reduce exposures.
112 It is not clear where 4.4% per Sv has come from and what it is.
117 There should be a reference to the 300 mGy threshold even if it is only a private communication.
118 A little more explanation is needed here. Are the life-time cancer risks after in utero irradiation, that are similar to those after irradiation in early childhood, additional to childhood cancers? The reader is being told that wTs cannot be provided for the fetus without perhaps having appreciated why there might be a need for them. The last sentence states: “Finally, for the reasons given in Publication 82, the Commission suggests that in-utero exposure should not be a specific protection case in common prolonged exposure situations where the prolonged dose is well below about 100 mSv.” Clarification is required.
123 In lines 3 and 8 would it be better to use Gy rather than Sv? These are discussions about epidemiological data.
8. ICRP Draft section 5 - The general system of protection
While it is understood that the emphasis should be on the source-related assessment, which is amenable to control, it is important that individual related assessments are also carried out to determine people’s overall exposure to all relevant sources of ionising radiation. This helps to provide perspective and provides information that studies have shown the public wants.
As discussed earlier, there is a need to clarify the situation regarding dose constraints and dose limits. Whilst clearly doses have always been optimised in a way complementary with the dose limits, the suggestion that dose constraints should be now used to limit doses rather than dose limits may cause confusion, particularly in non-specialist stakeholders. For example, in the emergency arena there is the potential to confuse further first responders such as the emergency services (eg, police and fire-fighters). The principles and numerical quantities might not have changed as such, but care is needed that these recommendations are communicated effectively. The statement in paragraph 132 regarding the dose constraints that ‘not maintaining these levels of protection should be regarded as a failure’ implies a dose limit and is stronger than the previous ICRP guidance on constraints. The discussion in paragraph 137 then seems to contradict this. Other statements such as in paragraphs 136, 163, 194 and 195 can all be taken to imply a need for a more restrictive regime than currently. They indicate that reductions in doses are required so they are as low as they can be – is this what ICRP intended?
Detailed technical comments on this section are given in Table 6.
TABLE 6 Technical comments on the general system of protection
129 Suggest insert “individual medical” before “… diagnosis or treatment;” in line 4.
130 Whilst the concept of only identifying and quantifying sources causing substantial exposures to the individual is clearly valid, should an attempt be made to clarify “substantial” further? Here and elsewhere the concept of “actual individuals” requires clarification as there are difficulties in calculating effective doses for specific people.
131 “Source-related” assessments might be of primary importance for occupational and public exposures, but they are not for medical exposures where both the benefits and the risks are entirely “individual-related”.
132-139 The principle of justification is not mentioned in this section, despite paragraph 18 saying that it is a prerequisite of the complete system of radiological protection. Is the principle of justification now to be completely excluded from the general system of protection, not just the methods for doing it for public and occupational exposures?
132 and 133 As discussed for S5, a dose constraint is not the most fundamental level of protection. The definition of a constraint is stronger than that in ICRP 60 and the idea that not meeting the constraints is a “failure” indicates that they are to be treated as a limit.
134 It is suggested that this paragraph is rather too negative in terms of occupational exposure, where, in practice, the total exposure (from controllable sources) is often assessed – as, in fact, it states in paragraph 144.
If the dose limits are to be retained then the numerical values should perhaps be given here.
Figure 2 It would help if the situation regarding doses from past controlled discharges was clarified here and in the text. NRPB has maintained that these doses should be included in the comparison with the dose limit but this is not stated here. Some of the illustrations in Figure 2 are confusing. For example, the inclusion of a picture of a patient undergoing radiotherapy treatment as one of the sources of “public” exposure, implies that the medical exposure itself is being treated as a “public” exposure, rather than the inadvertent exposure of nearby members of the public from the practice of radiology. This is misleading and it might be better to replace it with consumer products. It is also necessary to clarify what is meant by “normal situations”.
136 The fact that the maximum dose constraints for the public and workers are the same numerically as the dose limit and the changed definition of the constraint to be more like a limit could lead to confusion. This paragraph could be interpreted as implying that statutory dose limits should be reduced. It is logical that constraints for a single source should be lower than the dose limit for multiple sources but this needs to be clarified.
137 This paragraph is important and is supported by NRPB, but it could be said to contradict the idea of “failure” in paragraph 132. It also appears to relate to dose or risk constraints in emergency situations. This would seem to suggest that constraints in emergency situations are to act as upper Intervention Levels. This should be clarified.
139 The principle of “Optimisation of Protection” is introduced here as being complementary to the principle of “Limitation”. There is a danger that optimisation will not be seen as applying to medical exposures, since they are not subject to the principle of “Limitation” (see also comment on paragraphs 189-203).
140 Optimisation applies to existing exposure situations and not just practices.
142-148 Whilst the classes of exposure are unchanged since ICRP 60, clear reference to where emergency service personnel fit during intervention situations would be helpful.
143 The idea that not all exposure at work should be regarded as “occupational exposure” is a sound one. With reference to the point above on paragraphs 142-148: “exposures incurred at work …… the responsibility of the operating management”. Would employer serve as a more universal term?
144 This could lead to some confusion. For example, is the Commission saying that each x-ray set in a hospital is a different source requiring its own dose constraint. In most occupational exposure situations, there is only one (set of) source(s) and a dose constraint seems to have little relevance.
146 This paragraph does not make it clear that radiation exposures received by patients undergoing diagnosis, screening or therapy and by friends or relatives helping in the support and comfort of patients are regarded as “medical exposures” by ICRP. It needs to be clearly explained that, as ‘medical exposures’, they are not subject to the dose restrictions that apply to hospital staff or nearby members of the public who are inadvertently exposed to medical sources. Although all these classes of exposure and types of exposed individual are mentioned, the different ways in which they are to be controlled are not, and they do not all fit under the heading “Medical exposure”.
147 Suggest change last two lines to – “… rather to use the radiation to provide diagnostic information or to guide interventional procedures. Nevertheless, the dose cannot be reduced indefinitely without loss of essential information for making an accurate diagnosis or for completing an interventional procedure.”
148 The 1st sentence suggests that there is no room for constraints in medical exposures. In practice, concepts such as diagnostic reference levels (ie, constraints by another name) have a very important role, and it should be made clear that it is only “dose limits” that are not recommended for patients.
Again, there is no mention of the need to optimise the protection of patients. Suggest change 2nd sentence to – “The emphasis is then on the justification of the medical procedure and the optimisation of the protection of the patient.”
To clarify that patients are not regarded as “members of the public” in these recommendations, suggest change 3rd sentence to – “The quantitative individual dose restrictions do apply to workers in medical services and to nearby members of the public who are unwittingly exposed to medical sources of radiation.”
In the 4th sentence, it is not clear what changes of emphasis are needed for workers in medical services compared to any other radiation workers. The 6th sentence appears to be merely repeating much of the 5th, but fails to make the important point that the protection of carers is not treated in the same way as the protection of general members of the public.
149 The last two sentences (“The commission recognises …”) may be true, but represent a presumption by the commission. It is not for ICRP to speculate about the acceptance of its recommendations, nor of having “its hopes fulfilled”. The commission does not have to implement its own recommendations: indeed it deliberately refrains from prescribing how to go about their practical implementation. The wider radiation protection community does have to consider such practicalities, and their list of stakeholders does not include the Commission.
151 This paragraph is not needed.
155 Previous comments about the system of dose constraints apply here also. In fact, this paragraph provides no further guidance in terms of the application to operational and regulatory systems (ie, the heading of this section).