12. ICRP Draft Section 9 - Medical exposure
There appear to be no fundamental changes in the recommendations for protecting people from medical exposures in these draft 2005 recommendations compared to those in ICRP 60, ICRP 62 and ICRP 73. Indeed, much of Chapter 9 (Medical Exposure) is verbatim extracts from ICRP 73. However, the advice given in Chapter 9 is fragmentary, does not follow a logical order and is a confusing mixture of advice on how patient, public and occupational exposures from medical sources of radiation should be controlled. It would benefit from starting with a clear description of exactly what ICRP consider to be “medical exposures”. Previously in ICRP 60 and ICRP 73, only exposures of patients for diagnostic, therapeutic or medico-legal purposes and exposures of non-professional carers and volunteers in medical research programmes were regarded as “medical exposures”. The inadvertent exposures of nearby members of the public and workers from medical sources of radiation were not previously regarded as “medical exposures” and yet they are discussed under the heading ‘Medical Exposure’ in Chapter 9 (and Section 5.3.3) as though they were. Having defined what constitutes a “medical exposure”, a clear statement should be made that the basic principles of justification and optimisation (but not dose limitation) still apply to them. A brief review of the special ways in which the principles of justification and optimisation are to be applied to the three types of individual who can be subject to medical exposures (patients, comforters, and volunteers in research programmes) could then form the bulk of Chapter 9. As it stands, the optimisation of protection for patients is given so little attention in these draft 2005 recommendations, that the reader is left in considerable doubt as to whether ICRP still regards it as worthwhile.
Detailed comments on the section of the draft recommendations on medical exposure are given in Table 10.
TABLE 10 Technical comments on Medical exposure
213 Again, the need for optimisation of patient exposures appears to be neglected. Should not the 2nd sentence say – “The emphasis is then on the justification of the medical procedures and the optimisation of protection of the patient”?
The rest of the paragraph is merely a repeat of paragraph 148 and has nothing to do with ‘medical exposures’, so it is questionable whether it needs to be repeated here. If it is retained it would be much clearer if it read -
“The recommendations on dose limitation do, however, apply to the exposures of workers in medical services and to members of the public who are unwittingly exposed to nearby medical sources of radiation. It should also be recognised that some exposures might have to be incurred by members of the public in the care and support of friends or relatives who are themselves undergoing medical exposures. For these three types of exposed individual the appropriate constraints as discussed in Chapter 6.2 (not “Chapter 6.4”) should apply.”
214 The three issues raised in this paragraph (“Secondly”, “Thirdly” and “Finally”) appear to be totally unrelated to each other and the last one has nothing to do with “medical exposures”. The reader is left wondering what this apparently random list of issues has to do with ICRP’s recommendations on how medical exposures should be controlled.
215 “Procedures” would be better than “processes” in the 1st sentence and it is not only the “physicians” that need training but also the technicians (radiographers) that carry out and directly control most of the exposures. It is not clear why the need for training is dependent upon the fact that patient exposures are deliberate. If they were unintentional, there would surely be even more urgent need for training.
It would be better if the 3rd sentence ended – “… or to guide interventional procedures.”
The 4th sentence confuses exposure with dose and regulations with recommendations. It would be clearer as – “Limitation of the dose to the patient is not recommended, but the medical exposure needs to be justified and controlled by the physician, who therefore should be aware of the risks and the benefits of the procedures involved.”
216 It is confusing to use “radiological procedure” rather than “medical exposure” in this section, since ICRP (in both its title and its recommendations) uses “radiological” to mean ‘appertaining to radiation’ rather than ‘appertaining to medical radiology’.
4th sentence: Is not the ultimate aim of generic justification to judge that the benefits will usually outweigh the risks, rather than to merely judge that the procedure will usually be of some good, without any consideration of the risks?
5th sentence: Why leave it to this second level of justification before you have to demonstrate more good than harm?
217 Is “This procedure” the procedure of justification or the radiological procedure that has been justified? Either way, the requirement to keep doses as low as is consistent with the medical objectives has now become part of the justification and not the optimisation of the medical exposure. Is this intended? (see further comments on optimisation in paragraph 222).
219 Would it not be helpful to indicate that individual justification is not required for simple diagnostic procedures that have already been generically justified, as in ICRP Publication 73?
220 Would not Section 9.2 dealing specifically with pregnant patients be better placed after the more general section on optimisation of protection for all patients?
Should you not mention the very small risk of childhood cancer following in-utero medical exposures, otherwise there are no risks to tell the patient about in paragraph 221?
222 Change “patient doses” to “patients” in heading of Section 9.3 (you are protecting patients not doses).
1st sentence: If all medical procedures are per se “clearly justified”, there would be no need for ICRP to recommend that they should be justified. Suggest change to – “Most medical procedures causing patient exposures …” (as in ICRP Publications 60 and 73).
2nd sentence: Although the concept of “optimisation of protection” has been broadened in these draft recommendations, for medical exposures it surely still involves reducing unnecessary patient doses without compromising diagnostic or therapeutic effectiveness and taking social and economic factors into account? So why not state this clearly at the beginning of this Section (9.3) rather than under justification in paragraph 217?
223 Last sentence: The diagnostic reference level should surely be expressed as a readily measurable patient dose related quantity’? There are many readily measurable patient-related quantities that are totally unsuitable (eg, height, weight or inside-leg measurement).
225 1st sentence: suggest end with – “… is regarded by ICRP as a medical exposure.” This ‘definition’ of a ‘medical exposure’ would be better coming at the beginning of the chapter (see general comments at the beginning of this chapter).
3rd sentence: Their exposure is different from the inadvertent exposure of members of the public to medical sources because they are informed and consenting, and consequently the public exposure constraints and dose limits are inappropriate.
4th sentence: Did ICRP 73 state that a constraint in the region of a few millisieverts is likely to be reasonable, because it is easy to achieve in most circumstances without undue restriction on the care and comfort given or because it will result in a risk to the comforters that is small compared to the likely benefits to both the comforters and the comforted? Or both? The draft recommendations rightly say that higher constraints may well be appropriate for the parents of a very sick child. But, by setting the maximum dose constraint for comforters and carers at 20 mSv, is ICRP assuming that there are no foreseeable circumstances in which such a high dose will be incurred or that above this dose the risks will always outweigh the benefits? If the latter, then this involves a moral/ethical judgement about the sacrifice that an individual should make in the care of another person. ICRP should be careful that the maximum dose constraint for comforters and carers is not used or interpreted in this way.
226 Volunteers in medical research programmes and “patients” having diagnostic medical exposures for insurance or legal purposes, do not fit under the heading “Helpers and carers and the public”. These types of “medical exposure” should be clearly defined at the beginning of this chapter (see general comments) and the special ways in which their exposures are to be justified and optimised should be discussed under more appropriate headings.
Is it the responsibility of national authorities to set dose constraints for volunteers participating in research projects involving medical exposures? This is done at the local level in the UK, by Local Research Ethics Committees.
227 Inadvertent exposures of members of the public from medical radiation sources are not classified as “medical exposures” so if this paragraph is to remain in this chapter the title should perhaps be changed from “Medical Exposure” to “Exposures from medical sources of radiation”.
Last sentence: Radioiodine is also used to treat patients with thyrotoxicosis in sufficient quantities to require special restrictions on their contact with members of the public.
13. ICRP Draft Section 10 – Potential exposures
It would be very useful to give some indication at the start of this section of what it covers, including waste disposal and nuclear plant accident safety, etc. Other publications in the area are mentioned and quoted from but there is no general statement saying that the guidance in these documents still applies.
Much of the text is difficult to understand with terms such as “probability assessment” remaining undefined. The introductory text on this from ICRP 60 was much easier to understand and could have been used here. This section should either have been much shorter, simply referring to other documents, or have provided more detail summarising the important recommendations from the ICRP publications mentioned. For example, tables and figures from ICRP 64 could have been used to illustrate possible risk based constraints.
This section has not really addressed at all the issue of potential exposures for radioactive waste disposal. ICRP 81 considers two types of exposure scenarios following disposal: normal evolution of the site (involving waste degradation and eventual dispersion) and intrusion. For normal evolution the recommended limit is 0.3 mSv y-1 or an equivalent risk of 10-5 y-1. It is stated, however, that whilst it is possible to aggregate the probability of events and the dose, more information may be obtained for the decision-maker from separate consideration of the probability of occurrence of a particular situation and the resulting dose. Doses from potential intrusion are considered very differently. For circumstances where human intrusion could lead to doses sufficiently high that intervention on current criteria would almost always be justified it is recommended that reasonable efforts should be made to reduce the probability of intrusion. In connection with this ICRP 81 quotes a level of 10 mSv as being a generic reference level below which intervention is unlikely to be justified and a level of 100 mSv as the generic reference level above which intervention would almost always be justified. This also raises the issue mentioned in reference to paragraph 29: is it 10 mSv or 20 mSv?
TABLE 11 Technical comments on Potential exposures
228 It is not clear that the statement – “storage of waste rather than its dispersal will reduce normal exposures but will increase potential exposures” is always correct. It depends on what is meant by normal exposures. Storage of wastes would be expected to increase “normal” exposures to workers.
229 What is meant by a “probability assessment’”
231 This paragraph requires clarification.
232 Other ICRP publications (including ICRP 64) give a level of 0.1 Sv below which deterministic effects will not occur. Here a few hundred millisieverts is mentioned. Whilst clearly there is basic uncertainty on this value, if ICRP are recommending a system where there is a cut-off, then it would be helpful if they could choose a particular value for clarity.
233 Does this advice apply to protection of the public or just occupational exposure?
234 It is not clear whether this is still a recommendation or just a comment on what is in ICRP 76. Do the risk constraints still apply?
236 This paragraph is not clear and is open to different interpretations.
237 The issue of large accidents is very important. These are discussed in ICRP 64 and this should be referred to rather than simply referring to INSAG reports.
239 Again this paragraph is not clear, particularly what is meant by an “unconditional probability”.
240 This is not very clear and seems to ignore those situations where the particle is not “incorporated” such as those which might lead to skin damage. The use of the term incorporated is also unhelpful. Individuals may be exposed by ingesting a hot particle that may pass through the body unmodified (unincorporated!).
14. ICRP Draft Section 11 – The protection of the environment
It seems strange to include what will be done in a recommendations document. If ICRP are still formulating their recommendations on protection of the environment it would be better to state the principles they are adopting and the intended approach and leave everything else to a supporting document or future advice.
15. ICRP Draft Annex A – Nominal risk coefficients, etc
The main text of the draft ICRP recommendations refers to Annex A in a number of places and the Annex does address all of these points. However, the current version of Annex A is not easy to read and understand; in particular, various concepts are brought into Annex A in a haphazard way. It is not clear from a reader’s point of view what are the relationships between these concepts, or how they relate to the calculation of tissue-weighting factors, which is the objective of this Annex. It would be helpful if Tables A.1 and A.2 were presented early in the Annex. The meaning of each column and the calculated values within them could then be described. Related concepts such as nominal risk coefficients, uncertainty, lethality and detriment could be further discussed. This would make the Annex easier to read and understand.
TABLE 12 Technical comments on Annex on nominal risk coefficients, etc
A1 This paragraph is the only place where tissue-weighting factors are mentioned in the Introduction, but it fails to elaborate further on this concept. Some explanation of tissue-weighting factors is required since they form the key outcome of Annex A.
A2 and A3 Risk transfer modelling and data used in this modelling are described in these paragraphs. However, the way in which tissue-weighting factors are derived in relation to risk estimates and detriments is not described. The Introduction appears to be a collection of concepts without a clear link between them.
A5 What is the detriment adjusted risk coefficient? Is this an average over several detriments? What is the definition of loss of quality of life? How are these quantities combined? Some clarification is required when a new concept is introduced, or references should be given.
A6-A8 These paragraphs are dedicated to radiation risk modelling. They relate mainly to modelling of cancer incidence. How do they relate to the detriment-adjusted nominal risk coefficient and what is their relation to tissue weighting?
It would be better to start off with nominal risk coefficients, detriment and detriment adjusted risk, then describe how tissue-weighting factors are derived from these quantities.
A10 The purpose of the last two sentences requires clarification.
A11 Were the sizes of the selected populations taken into account in computing the nominal risk estimates? What does an “un-weighted average was calculated to form a composite population” mean? Precisely what was averaged?
A14 The liver cancer risk appears to be a very rough estimate. Was there any quantitative evaluation to achieve this result? A reference should be given if more detailed work is presented elsewhere.
“In ICRP 60, the liver cancer risk estimate was based on estimates derived from studies of patients injected with the radioactive contrast medium Thorotrast, for which generalisations to low LET radiation exposures are problematic.” What does this mean? If the generalisation based on the Thorotrast data is problematic, is ICRP suggesting that the reverse is true when applying risk estimates for low LET radiation to alpha exposures?
A17 Insufficient information is given in this paragraph to support the quantitative estimate for hereditary risks. A reference (eg, UNSCEAR, 2001) should be cited here.
A18-A22 Since Section A.3.1 on Uncertainty and sensitivity analyses refers to DDREF, it would be better placed after the following section on DDREF. In both sections, reference is made to reports that give quantitative estimates of uncertainties. Why not quote the values from these reports?
Table A1 A list of lethality values q for various cancers is shown in this table. How were those lethality values derived? References should be given if more detailed work is presented elsewhere. What is the relative cancer free life lost? (For skin cancer, this value is 1. What does this mean?) How is detriment calculated? It appears to be the product of the lethality adjusted nominal risk and relative cancer free life lost.
Staff of the NRPB have carefully considered the draft 2005 recommendations of ICRP and a number of comments and suggestions for improvements have been made in this report. NRPB staff welcome the intention of ICRP to consolidate its previous recommendations and supports the idea that the basic dose limits laid down in previous ICRP publications still apply. It is important that the ICRP recommendations are clearly stated and that they have practical application. In particular, the recommendations should cover the basic ICRP principles of justification, optimisation and limitation. The distinction between dose limits and constraints should also be clarified and explained and the basis for the recommended maximum dose constraints requires further clarification.