|7 September 2006
Comments on ICRP 2006 Draft Recommendations
NCRP appreciates the opportunity to offer comments on the 2006 Draft Recommendations. The following comments are submitted on behalf of the Officers of NCRP by Kenneth R. Kase, Sr. Vice President.
The value of publishing this revision of the ICRP recommendations is clear.
In general, the 2006 draft is an improvement over the earlier version of the document, and addresses many of the suggested additions and clarifications. However, it is essential that the 2006 recommendations contain a section (or perhaps an Annex) that summarizes the changes in recommendations relative to ICRP Publication 60. This summary should consist of both a concise narrative description of the changes, and a table that lists them.
The draft is very clear in several places that the assumption that the risk of detriment is proportional to dose at low doses is used only to make judgments related to the control of radiation exposures. However, it might help to put that statement, along with a statement that the risk values quoted and used for radiation protection purposes are not appropriate for determining the risk to individuals or specific populations for specific exposure situations, at the very front of the draft.
The use of deterministic, tissue reaction, stochastic and cancer/heritable disease is still inconsistent. The statement in 29 indicating that tissue reactions are also called deterministic effects is an improvement over the previous version. However, in 88 it is stated “tissue reactions (sometimes also, but less precisely termed deterministic effects)”. The term “deterministic effects” is no less precise than “tissue reactions”. In 356 “non-stochastic (causing tissue damage)” is used. There are other similar examples.
The concepts of exclusion and exemption (Section 2.4) lack a solid basis; the arguments offered in the draft are less than convincing. These concepts need to be put more clearly into the framework of the three fundamental principles of radiation protection.
Section 3 Biological Aspects of Radiological Protection is generally clear and the conclusions and recommendations are well-supported.
The stability of the dosimetric quantities as described in Section 4 is appreciated.
Overall Section 5, The System of Radiological Protection of Humans is clear. The discussion of dose constraints for individual sources has been extended relative to the earlier draft document. The definition of bands of projected exposures given in the text and the examples given in Table 4 will be useful to authorities who must define the levels of dose constraints for various types of sources of occupational and public exposures. However, there is some concern about the specification of “single source”, Section 5.1. For many occupationally exposed workers who receive their entire doses from a single source (the most common case) the constraint should be the same as the limit. ICRP should explicitly state this in the recommendations. Also, it is not clear how much of an improvement has been afforded by the new concept of “representative individual” over “critical group” (Section 5.4.3).
There seems to be considerable confusion about the intent of ICRP with respect to protection of the environment (Section 10). There is a need to develop general principles for protecting plant and non-human animal species from radiation. The metrics upon which radiation damage to the natural environment is assessed also need to be defined in a clear and functional manner. ICRP needs to do more than try to define reference species as indicators of radiation effects in various natural environments. These efforts should be carried out before statements such as those in Section 10 of the draft ICRP recommendations are included in the document.
There are a few areas that have been neglected and need attention.
1. The field of fluoroscopic interventional procedures is not adequately addressed in Sections 4, 5 and 6. This is an area in which tissue reactions cannot always be prevented, dose constraints may be impossible to establish and exposures can be difficult to assess.
2. Exposure to cosmic rays related to air travel and space activities is not discussed.
3. It is not clear how radiation exposure related to military activities and human space exploration and travel relate to the system of protection.
There are significant typographical, spelling and grammatical errors in the text. Careful editing is needed.
Section 1. Introduction
ICRP points out in 12 that there are no fundamental changes needed to the system of radiation protection, there is more continuity than change in the recommendations and the revised recommendations suggest no changes. This has raised questions about whether there is a need for this revised set of recommendations. However, 11, 14 and 15 clearly explain the need for a new publication to consolidate recommendations promulgated during the past 15 years and bring them into a consistent framework supported by a series of recently published and soon to be published foundation documents. There is value to publishing a revision of the ICRP recommendations at this time.
22: The emphasis in this paragraph on using appropriate data for retrospective risk estimates and detriments related to specific exposures is important and welcome.
Section 2. Aims and Scope of the Recommendations
29 and 30: LNT is better described as a model used to extrapolate the dose-effect data from high doses to low doses than as an hypothesis. ICRP is to be commended for stating the limits of applicability of LNT, i.e. to managing risk from radiation exposure, and how this leads to the fundamental principles of protection. These statements together with those in 22 should be prominent in the introduction to the draft. The statement indicating that tissue reactions are also called deterministic effects may be an improvement over the previous version. However, tissue reactions can also be late effects or permanent. In severe accidents and in many cases following radiation therapy, they are permanent.
33: There should be a lower dose value below which optimization is no longer necessary because a dose value has been reached that is insignificant for protection purposes, e.g. an annual individual dose of 10 ìSv.
40: The intention of this paragraph is not clear. There is no definite resolution to the terminology problem. Does ICRP intend to continue the use of the term practice, or not?
41 through 46: The concepts of exclusion and exemption lack a solid basis; the arguments offered in the draft are less than convincing. The terms amenability and necessity are ambiguous. It is not clear if ICRP intends that the Principles of Justification and Optimization are to be applied to determine whether a source is amenable or necessary to control. It seems that these Principles should be applied before a source is arbitrarily excluded or exempted from regulation. If this is done, sources that result in an annual dose higher than the negligible value of 10 ìSv may be able to be exempted or excluded from regulatory control. (The exposure has been justified and optimized and there is nothing more that regulatory control can achieve.) 46 seems to permit this more flexible approach with the statement, “… National regulators should decide the criteria for exemption on a case-by-case basis and the dosimetric boundary of 10 µSv/y should be only one of the criteria used.” This latest statement makes the most sense and it should be emphasized first to avoid confusion.
Section 3. Biological Aspects of Radiological Protection
This section is generally clear and the conclusions and recommendations are well-supported.
56: As mentioned above, LNT is better described as a model used to extrapolate the dose-effect data from high doses to low doses than as an hypothesis.
57: The statements in this paragraph on the appropriate use of the LNT model are very important to emphasize.
60: Epidemiological studies related to low dose or protracted exposure may have enough statistical uncertainty to limit their use for estimating risk factors, but they do demonstrate that there is no discernable cancer causation below some dose. ICRP would do well to acknowledge this fact.
Section 4. Dosimetric Quantities
116 and 117: It should be emphasized that these two paragraphs describe calculations that would be made only for comparison with a recommended effective dose or regulatory limit and not for assessment of risk to an individual.
120: It is stated that the equivalent dose to the remainder tissues is computed as the arithmetic mean of the equivalent doses to the tissues listed in the footnote to Table 4.2. It seems that the equations 4.6 should each have a multiplicative constant of 1/13.
132 and 133: There may also be situations in which external exposure is very non-uniform and measured by using multiple dosimeters. In such cases equation 4.10 may provide a poor estimate of the effective dose.
137: The statement that, “Care has to be taken in such situations so that no (emphasis added) tissue reactions occur” only applies to situations in which dose limits are stated (e.g., occupational exposures). This approach is consistent with one of the objectives of radiation protection as stated in section 2.3 of NCRP Report No. 116 (1993), i.e.,
to prevent the occurrence of clinically significant radiation-induced deterministic effects by adhering to dose limits that are below the apparent threshold levels.
However, 137 addresses medical exposure of patients; a practice in which dose limits do not apply (see 186). In radiation therapy and in fluoroscopically guided interventional procedures tissue reactions may be inevitable and, therefore, the prevention of tissue reactions may not be practical. More appropriately, it should be stated that care should be taken to minimize them.
138: This paragraph does not contain the kind of clear guidance expected of ICRP and it appears to be at odds with 144. The assessment and interpretation of effective dose from medical exposure of patients is more than problematic. As stated in 144 it is, “…completely inappropriate” in cases of high doses that give rise to tissue reactions. Medical exposure of patients is the main source of high doses and, therefore, it should be stated clearly that the use of effective dose is completely inappropriate for these types of medical exposures. Perhaps ICRP should go even further in this area and, for the same reasons that effective dose is not appropriate for use in epidemiology studies (see 142 and 143) state that the use of effective dose for medical exposures of patients is also inappropriate.
139 through 144: These paragraphs on the application of effective dose are extremely important and perhaps deserve greater visibility in the draft.
145: The quantity “person-sievert” is widely used and more appropriate.
146 and 147: These paragraphs on the application of collective dose are extremely important and perhaps deserve greater visibility in the draft.
Section 5. The System of Radiological Protection of Humans
161: The characterization of all the x-ray equipment in a hospital (and possibly research institutions as well) as a single source is problematic when applying a dose constraint to a single source. If it must be assumed that an individual can be continuously exposed to that source, i.e. all the x-ray equipment, it could be interpreted that each individual piece of equipment would need to be shielded so as to maintain the dose from that piece to a small fraction of the constraint. This could require excessive shielding for each individual x-ray unit.
168: The important category of fluoroscopically-guided interventional procedures should be explicitly included.
175 and 176: One wonders how much of an improvement has been afforded by the new concept of “representative individual” over “critical group,” especially when the definition is not clear and Publication 101 is not available (and not included in the References).
188 through 191: There are three principles articulated and two of them are discussed in independent sections of the draft, 5.8 and 5.9. It is not clear why the third principle is relegated to two subsections, 5.7.1 and 5.7.2, instead of being discussed in an independent section.
192: Although constraints may be used in the optimization process, they are not part of the Principle per se as articulated in Section 5.7. They are only one method, among others, of restricting dose or risk to an individual. Constraints should be removed from the first sentence.
198: It must be made very clear that dose constraints are intended to provide guidance for optimization and should not be specified in regulations or legislation.
197: The point made here concerning the prospective nature of constraints is very important.
198: Source-related dose constraints may remove some of the inequity in the optimization of radiation protection. However, the overall objective of both the ICRP and NCRP dose-limit recommendations is to control the lifetime risk to the maximally exposed individuals. Therefore, the cumulative dose limit could be viewed as “the most fundamental level of radiation protection” (also in 184).
203: The reference to Table 4 is incorrect. It should be Table 5 and the Table on pg 61 should be renumbered.
205: There is some confusing language in this paragraph. The word “benefit” is used in two different contexts. In line 2 it connotes a tangible benefit, such as a job and paycheck, to the person exposed. In line 5 it simply indicates that the exposed person has been informed of the hazards of radiation and received training to mitigate those hazards. This second use of “benefit” is not meant to be the benefit referred to in Line 2. Perhaps this can be alleviated by replacing “benefit from” in Line 5 with “have received”.
198 through 209: Regarding the use and specification of constraints the issue of exposure during fluoroscopically-guided interventional procedures in medicine does not fit either category, planned or emergency situations. Neither the dose to a particular patient nor the dose to staff can be estimated in advance due both to uncertainty in the dose from each procedure and uncertainty in the number of procedures in a particular time period. The doses to staff, particularly physicians, performing such procedures are not amenable to planning.
Section 6. Medical Exposure of Patients
General: The important category of fluoroscopically-guided interventional procedures is not mentioned.
259: It should be explicitly stated that conformance with diagnostic reference levels, by itself, should not be taken as assurance that optimization has been achieved.
270 through 276: These paragraphs do not all address the issue of release of patients. Perhaps the title for Section 6.5 should be “Precautions for the use of unsealed radionuclides in nuclear medicine procedures”.
Section 7. Exposure to Natural Sources
284: Exposure to cosmic radiation is enhanced with air travel and space exploration. The draft should recognize and discuss the control and regulation of exposure to cosmic radiation in these situations.
295: There seems to be no basis for the apparent exemption dose rate of 1ìSv /h at a distance of 0.1 m. It is not in Section 2.2.
Section 8. Potential Exposures
This section is necessarily very general and non-specific. It presents the concept of potential exposure, but little detail about how one would estimate such exposures or apply the concept. It is not clear how the concept of potential exposures is applicable or helpful for protecting against accidents in radiation therapy (Section 8.6).
Section 9. Emergency Situations and Existing Situations
Section 10. Protection of the Environment
There seems to be considerable confusion about the intent of ICRP with respect to protection of the environment. The environment appears to be limited to plant and animal species and only risks associated with radiation exposure are considered. Environmental impacts related to radiological protection may be caused by activities related to reducing radiation exposure to humans. This is alluded to in 352, but could be stated more clearly so that the reader understands that such activities will be seriously considered when discussing protection of the environment and the impact of ICRP’s recommendations.
By including the discussion of protection of the environment in this draft there is an implication that the protection of animal and plant species will be incorporated under the system of protection that has been promulgated for humans applying the same three principles, justification, optimization and limits.
There is a need to develop general principles for protecting plant and nonhuman animal species from radiation. These principles should be consistent with, but may not be identical to, those for protecting humans. The metrics upon which radiation damage to the natural environment is assessed also need to be defined in a clear and functional manner. Without these metrics and methods for applying them, there cannot be a solid framework for implementing radiation protection of the environment and natural biota.
ICRP needs to do far more than try to define reference species as indicators of radiation effects in various natural environments. This effort should be carried out before statements such as those in Section 10 of the draft ICRP recommendations are included in the document. ICRP needs to state that it is in the preliminary stages of investigating the construction of a framework under which it can develop recommendations for protecting animal and plant species from harmful effects of radiation.
Section 11. Implementation of ICRP’s Recommendations