|U.S. Department of Energy Comments:
International Commission on Radiological Protection (ICRP)
2006 Recommendations for a System of Radiological Protection
September 13, 2006
The U.S. Department of Energy (DOE) appreciates the opportunity to review and provide comments on the International Commission on Radiological Protection’s (ICRP) 2006 Recommendations for a System of Radiological Protection. We note and very much welcome ICRP’s commitment to greater transparency in developing and seeking stakeholder views on its Recommendations. DOE has commented on previous versions of the Recommendations, both as an independent agency to express DOE-specific views, and through the U.S. Interagency Steering Committee on Radiation Standards (ISCORS) to provide U.S. consensus-based viewpoints.
The ICRP stated three aims for revising its Recommendations. The ICRP also broadly cited the importance for stability in international and national regulations in revising the Recommendations. Our viewpoints are provided in the context of these aims, and provide our insights on how the ICRP Recommendations can best meet the health and safety needs of national and international radiological protection. Viewpoints are offered in five principal areas of the Recommendations: dose constraints and limits; guidance for collective dose; use of new biological and physical information; exclusions and exemptions; and protection of non-human species and the environment.
Dose Constraints -
Our first key observation is that ICRP should provide clarification of its use of dose constraints and their application within a radiation protection framework. For context, DOE applies dose constraints in combination with an all-sources, all-pathways primary dose limit of 1 mSv/year. In DOE, dose constraints are applied as a starting point within ALARA analysis to ensure that individual sources are optimized and do not contribute more than a fraction (e.g., typically well below one-third; usually a few mrem/year or less) of the primary dose limit.
As an example, our DOE occupational radiation protection programs use the ALARA process and a hierarchy of administrative controls to help maintain worker dose significantly below DOE and ICRP limits. For perspective, the 5 year average annual dose (TEDE) to workers with measurable exposure is 0.74 mSv.
ICRP’s use of dose constraints “providing a fundamental level of protection” that are not to be exceeded, “and where action is almost always warranted,” confuses the relationship of constraints and dose limits and is inconsistent with the way DOE and others within the U.S. use these concepts. Therefore, it would be helpful for ICRP to clarify how constraints and limits are applied to optimize protection from one or more sources & to ensure that adequate protection for an individual is achieved.
Collective Dose -
Our second key observation is that more specific guidelines for implementing collective dose should be provided in the ICRP Recommendations. Collective dose takes into account a group of persons exposed and their period of exposure over a specified time. It is useful for getting a sense of the potential number of health effects to a population. Collective dose is recognized by ICRP as a useful tool in the optimization process for decision making and for comparing several options. The ICRP states that limiting conditions need to be set for collective dose. However, the Recommendations do not go further in providing specific guidance beyond these points.
DOE therefore recommends that additional specific guidance and boundary conditions for interpretation of collective dose in analysis and decision making are needed. Some examples are offered below:
•Data Quality Objectives (DQOs) are needed relative to the purpose of the evaluation. Is collective dose being used to support the development of a national policy or regulation? Smaller, facility-specific evaluations? Comparison of alternative technologies or remedial actions?
•Appropriate integration periods for long-lived radionuclides need to be provided. For example, over how many future generations (less than 200 years; greater than 1,000 years)? How does one deal with the large uncertainties presented with increased exposure and evaluation periods?
•Guidance on appropriate geographic areas. For example, they could be small for evaluating specific facility footprints, or larger to account for documented off-site transport of contamination (e.g. agricultural products in local areas that are then transported nationally for consumption).
Physical and Biological Information -
Our third viewpoint is offered relative to the ICRP’s use of new biological and physical information. This information is important in providing the underlying basis for parameters (e.g., radiation weighting and tissue weighting factors; risk coefficients for cancer and hereditary disease) used in calculation of dose and risk.
We noted the absence of any evaluation or inclusion of new information coming out of DOE’s Low Dose Program, which has the potential for significantly increasing our understanding of radiation effects. We suggest that these results, some of which are already available, be considered prior to moving forward with these Recommendations.
Changes in weighting factors and risk coefficients generally have the greatest potential for impacting regulations and regulatory guidance and their supporting dose and risk calculational approaches by national authorities.
We suggest that revision of weighting factors and other parameters may be premature, in that analysis of underlying data such as the latest A-bomb cancer incidence data that is not yet complete or formally published.
Exclusion and Exemption -
Our fourth key observation is that ICRP should continue to work on clarification of its terminology and application of exclusion and exemption. These appear to be addressed “stand alone” rather than systematically through the application of justification, optimization, and limitation principles.
Exclusions represent those actions taken a priori, thus bypassing the control of a practice. In this regard, the ICRP’s conclusion that “some sources are simply not amenable to control” appears arbitrary. As an example, control of cosmic radiation exposures to flight attendants and pilots could be amenable but just not very feasible. It is sometimes difficult to know with certainty a priori and implies that some forms of control may be excluded without any systematic assessment through use of the ICRP principles.
The description on the application of these terms implies that they are only appropriate when doses are very low or trivial. In fact, relatively higher doses may be acceptable.
Like exclusions, exemptions represent an a priori action on a practice, as well as those actions taken after cessation of control for a practice; it can also be clearance. For exemptions, optimization efforts may reach a condition or optimal point where there is minimal value added achieved from the ALARA analysis process (e.g., there is no or very little incremental dose reduction).
Radiation Protection of Non-Human Species -
Lastly, the ICRP’s consideration of radiation protection of non-human species appears to lack a clear priority and consensus on the path forward presented. There is no discussion of a policy or framework for protection, as was stated early in the introduction of the Recommendations. Only a description of the ICRP’s on-going work to develop standard reference organisms is presented. There is no clear consensus on the basis for and ICRP’s selection of the reference organisms for which detailed dosimetry is now being developed by ICRP.
As we have suggested in comments on previous Recommendations and supporting foundation documents on this subject, we suggest that the ICRP’s priority should first be placed on defining the protection policy and benchmarks for demonstrating protection. The policy should be commensurate with the perceived risk to non-human species in specific exposure situations (e.g., in cases where man is removed from exposure due to controls or restrictions, but exposure pathways to biota remain). Rational, consensus-based benchmarks (e.g., dose rate guidelines of 10mGy/day and 1mGy/day previously recommended as safe for populations of biota by IAEA and UNSCEAR; other criteria) need to be re-affirmed or defined for demonstrating “protection.” And on this we must define what it is we are trying to protect (e.g., populations vs. individual organisms; if it is appropriate to apply sub-cellular and sub-individual effects as an indicator of effects to individuals and to populations).
The DOE has been successful in developing practical and rational approaches with the involvement of our field and operations experts, and with our regulatory compliance stakeholders. The Department’s Graded Approach for Evaluating Radiation Doses to Aquatic and Terrestrial Biota (DOE Technical Standard DOE-STD-1153-2002), and its supporting implementation tool RESRAD-BIOTA, provides cost-effective screening methods as well as methods for more detailed evaluations where needed. Finalized in 2002, the DOE Graded Approach is now widely implemented across DOE and by several state and federal agencies, and is being applied internationally. We continue to suggest that a graded approach philosophy employing screening tools for practical, cost-effective demonstration of protection and supporting reference organisms be included in any approach advanced by ICRP for protection of non-human species.
Comments on Specific Text –
Some comments on specific text of the Recommendations are provided below.
•Paragraph 58, “The Commission also notes that since the estimation of nominal cancer risk coefficients is based upon direct human epidemiological data, any contribution from these cellular phenomena would be included in that estimate.” This sentence should be deleted. It is not clear why processes that occur at low doses would necessarily be reflected in risk estimates based on high dose exposures, particularly if these processes are dose dependent (see the last sentence of this section). In addition it seems that the application of a DDREF to convert the risk estimate for solid tumors determined at acute high doses to one that applies to low doses and dose rates is itself recognition of the impact of cellular phenomena.
•Paragraph 65: “Although there continues to be no direct evidence that exposure of parents to radiation leads to excess heritable disease in offspring, the Commission judges that there is compelling evidence that radiation causes mutation in reproductive (germ) cells in experimental animals.” In this section, the lack of evidence for hereditary effects of radiation in human populations is dismissed because of the presence of animal data showing hereditary effects of radiation. However with regard to cancer risk, cellular and animal effects such as bystander effects, adaptive response and genomic instability are dismissed in favor of epidemiological effect in human population (see section 58). This reason for the different approach in assessing risk for these health effects should be explained.
•Paragraph 120: “The equivalent dose to the remainder tissues is computed as the arithmetic mean of the equivalent doses to the tissues listed in the footnotes to Table 4.2.”
•As stated above, the remainder is to be computed using the arithmetic mean of the equivalent dose (H) of the remainder tissues (RT). However, formula 4.6 (listed above) set the HRT equal to the sum of the remained tissues. The inconsistency between the text in section 120 and formula 4.6 should be resolved.
•Paragraph 183: “It is rarely possible to assess the total exposure of an individual from all such sources.” The basis for this statement is unclear – at least for occupational exposure in the United States. It is normally expected that all sources of occupational exposures would be monitored using personal monitoring techniques such as dosimeters or bioassay for exposures anticipated to exceed the monitoring threshold. Accordingly, this statement should be changed to “In many cases it is difficult to assess the total exposure of an individual from all such sources.”
•Paragraph 330: “The quantitative recommendations given above should be used at the planning stage as the basis for developing operational intervention levels.” Either the location of the quantitative recommendations in the text or a citation in a published document should be provided.
We appreciate the opportunity to contribute to the evolution of the ICRP Recommendations through participation in the review and comment process. The 2006 version of the Recommendations shows a significant change in response to comments received during consultation on the previous draft Recommendations. However, it is still not clear that the ICRP has achieved the primary objectives for these Recommendations – specifically:
•to take account of new biological and physical information and of trends in the setting of radiation safety standards;
•to improve and streamline the presentation of the recommendations; and
•to maintain as much stability in the recommendations as is consistent with the new scientific information.
ICRP Recommendations are intended for use by all countries, regardless of the effectiveness and maturity of the system of radiation protection in that country. However, in countries with mature radiation protection infrastructures in which radiation exposure is maintained well below national as well as ICRP recommended limits, the need to modify current practices may not be apparent, particularly if the underlying radiation protection goals of the ICRP Recommendations are reflected in the national radiation protection system.
To partially ameliorate this problem in the future, it may be useful for draft recommendations to be issued on more limited topics at more frequent intervals, possibly following publication of the research and foundation documents supporting the Recommendations. In this way it would be possible to address and resolve Recommendations on one or two aspects of the radiation protection system when the underlying technical basis is mature without affecting other aspects of the radiation protection system.
From our involvement in the review and comment process, and in consultations with other regulatory agencies within the U.S., it remains a question as to whether or not the proposed refinements contained in the 2006 Recommendations are substantial enough to warrant replacement of the existing Recommendations. Specific themes supporting this viewpoint are highlighted below.
First, ICRP’s extensive review of data on health effects has not indicated that any fundamental changes are needed to its system of radiological protection. Existing numerical recommendations in guidance given since 1991 remain generally valid. Much of the material describes radiological protection practices already being implemented within many radiation protection programs within the U.S., to include DOE. Based on no significant changes in radiation risks, there doesn’t appear to be a strong public health and safety rationale to issue revisions to the Recommendations.
Second, the benefits of the new Recommendations may not outweigh the costs. Changes to regulatory and operations programs could be costly. And there are costs associated with educating stakeholders on why the changes were made even though the existing Recommendations have afforded us with a high degree of protection.
Finally, we note that the 2006 Recommendations are an improvement over the 2005 and earlier versions. But inconsistencies and “works in progress” remain and should be addressed before proceeding. New concepts must have clear international review and final consensus prior to being included. Examples of this key point include the presentation of exemptions and exclusions and their foundation documents; protection of non-human species and their foundation documents; and completion of analyses on the underlying biological and physical data that supports revision of dose and risk parameters and publication of this information.
DOE comments prepared and consolidated by: Stephen Domotor (Stephen.Domotor@eh.doe.gov)