Dr Patrick Smeesters
MD, Senior expert in Radiation Protection, FANC Lecturer (UCL, ULB)
Member of Euratom Art 31 Group of Experts Member of Belgian delegation to UNSCEAR
Abstract
Current regulation in radiation protection of the population is often based on the recommendations of the International Commission on Radiological Protection (ICRP), up to now the leading group in the fi eld. At the EU level, according to the Euratom Treaty, the directives are adopted by the Council, on a proposal from the European Commission (EC). To elaborate these proposals, the EC is assisted by a group of independent scientifi c experts referred to in Article 31 of the Euratom Treaty. This group of experts is the unique scientifi c group offi cially in charge of advising the EC as regards the Basic Safety Standards for the protection of the health of the workers and of the general public against the dangers arising from ionizing radiation. The EC organizes yearly, with the help of the RIHSS WP (Research Implications on Health Safety Standards), scientifi c seminars on relevant topics. In 2004 and 2006, these seminars consisted of critical reviews of drafts of the new ICRP recommendations, in the light of new scientifi c evidence. Globally major concerns were expressed regarding the question whether ICRP underlines enough the uncertainties and adopts suffi ciently the precautionary approach. These concerns still exist when looking to the fi nal text of the ICRP recommendations (ICRP Publication 103). As recent scientifi c evidence calls for regulatory action, the national regulators should take their responsibilities.
32
The international elaboration of the Basic Safety Standards
Current regulation in radiation protection of the population is mainly elaborated through a sequence of stages, beginning with scientifi c research, followed by global evaluations by organisations like the United Nations Scientifi c Committee on the Effects of Atomic Radiation (UNSCEAR) or the BEIR (Biological Effects of Ionizing Radiation) Committee of the US National Academy of Sciences, this process ending in recommendations by the International Commission on Radiological Protection (ICRP), up to now the leading group in the fi eld. All or part of these recommendations are then generally transposed into European directives, setting the mandatory safety objectives for the European Union (EU) Member States, and into the international Basic Safety Standards, jointly sponsored by the International Atomic Energy Agency (IAEA), the International Labour Organisation (ILO), the Nuclear Energy Agency of the Organisation for Economic Co-operation and Development (OECD/NEA), the World Health Organization (WHO), the Food and Agriculture Organization (FAO) and the Pan American Health Organization (PAHO). This international genesis gives guarantees of validation and consolidation and obviously favours harmonisation but, on the other hand, entails risks of inbreeding, political infl uences and “pseudo”-consensus: it is much more comfortable and safe to follow this (impressive) herd.
At the EU level, according to the Euratom Treaty, the directives are adopted by the Council (with qualifi ed majority), on a proposal from the European Commission (EC). To elaborate these proposals, the EC is assisted by a group of independent scientifi c experts referred to in Article 31 of the Euratom Treaty. This group of experts is the unique scientifi c group offi cially in charge of advising the EC as regards the Basic Safety Standards for the protection of the health of the workers and of the general public against the dangers arising from ionizing radiation.
Being aware of this responsibility, the Art 31 experts have elaborated a code of Ethics that can be seen as an expert’s deontology ensuing from social expectations regarding competence, neutrality and objectivity. According to this code, the experts shall give priority to the protection of public health. They may express views on political, economical, fi nancial, and liability matters but the health and safety considerations must always be
33 clearly identifi able in their opinions, proposals, guidance and statements.
Again according to the code, “the experts shall take the necessary steps to update and to broaden their scientifi c knowledge, in relation with any major issue possibly affecting radiation protection. With this aim in view, they shall maintain close contacts with the scientifi c world in the relevant matters. They shall use adequate means to take into account all the available scientifi c information and to avoid inappropriate selection of the sources”. Finally, “the experts shall avoid creating confusion between purely scientifi c judgments and value judgments on ethical issues that are often deeply interwoven in the scientifi c evaluations and may not be directly apparent. They shall avoid trying to arbitrate ethical issues. On the contrary, they shall try to recognize the more or less hidden ethical aspects and to bring them into light for those who have to make a decision”. Such code of ethics should be adopted by all scientifi c experts advising regulators on public health issues.
To help realizing these objectives, a Working party, called the RIHSS WP (Research Implications on Health Safety Standards), has been set up within the Art 31 group of experts with the task of helping to identify the potential implications of recent research results or new data analysis on the Basic Safety Standards Directive (and on the related recommendations and guidance). This Working party organizes on a yearly basis scientifi c seminars where leading experts are asked to synthesize clearly the state of the art in a particular fi eld. Additional experts, identifi ed by members of the Article 31 Group from their own country, take part in the seminars and act as peer reviewers. The Commission convenes the seminars on the day before a meeting of the Article 31 Group, in order that members of the Group can discuss the potential implications of the combined scientifi c results. Proceedings are then available on the EU web site (collection Radiation Protection).
EU Conference, Luxembourg, 4 November 2004:
A critical review of the draft ICRP Recommendations
In 2004, the ICRP offered for public consultation a Draft of its future Recommendations (Draft 2005 ICRP Recommendations). To perform a critical review of this draft, the EU Commission organized, with the help
34
of the RIHSS WP, a Conference that took place in Luxembourg on 4 November 2004. A list of Highlights of this Conference have been identifi ed and submitted to ICRP. While not being an exhaustive list of all the issues brought up during this Conference, these highlights had to be regarded as major and pertinent issues that were discussed during the Conference and should be provided to ICRP for consideration. Some major topics from these highlights are explained hereafter.
Regarding biological issues, a fi rst concern was related to the new risk coeffi cient for radiation induced hereditary diseases. When evaluated on comparable bases (risk for the fi rst generation, for 2 generations …), the genetic risk is in fact not reduced in the UNSCEAR 2001 Report by comparison with the previous UNSCEAR Report. Nevertheless, based on the existence of large uncertainties, ICRP took the effect on the generations farther than the second as being zero. This decision has been challenged as being not a balanced acceptable position based on the present scientifi c knowledge. According to the invited speaker (Prof. B. Dutrillaux), the main problem should be the radiation induction of small deletions leading to recessive mutations and diseases of which the phenotypes might frequently not be recognized by the physicians. Such cumulative small genetic disorders may propagate in the future generations with the risk of leading to more important pathological consequences. This was not taken into account by ICRP in the risk coeffi cient, as it is of the opinion that the major contribution to the genetic risk comes from large deletions expressing themselves essentially in the fi rst two generations. The basic question was whether we know enough about the radiation induced hereditary effects to close the matter.
Another important biological issue was whether the persisting uncertainties and the new experimental evidences in the fi eld of the effects of in utero exposure (exposure of zygotes, genetic susceptibility to congenital malformations, subtle IQ effects…) were suffi ciently emphasized and taken into account in the draft 2005 ICRP recommendations. In particular, the reduced attention for the protection of pregnant women, for instance in the section concerning the medical exposures, has been challenged.
35 Other issues were the validity of a DDREF of 2 and how differences due to age and gender were taken into account, particularly in the calculation of effective doses.
Some value judgments made by ICRP have also been challenged:
insuffi ciency of precautionary approach, management of uncertainty, lack of equity, limited consideration of genetic susceptibilities even in high doses situations …
As well FANC/AFCN as ABR/BVS have repeatedly expressed the same kind of criticisms during the public consultations organized by ICRP regarding its successive drafts of recommendations.
EU Scientifi c Seminar, Luxembourg, 17 October 2006:
New Insights in Radiation Risk and Basic Safety Standards
Recently, ICRP issued a third draft of Recommendations for public consultation. The purpose of the 17 October 2006 seminar was to review this new proposal in the light of current insights in radiation risks. The programme of this one-day seminar covered a large scope of issues1 and is reproduced hereafter:
1. Radiation-induced cancers and age/gender sensitivities
• New models for evaluation of the radiation-induced lifetime cancer risk: M. Little
• New epidemiological data (nuclear workers, Techa River): E. Cardis
• Large scale indoor radon studies (including leukemia):
M.Tirmarche
• Biological aspects in relation to age/gender sensitivities and discussion of the potential implications:
W.-U. Müller
• New biological data in relation with low dose risk:
D. Averbeck
1 Proceedings of the EU 2006 Seminar available on the web site of the EC:
Radiation Protection no. 145
http://ec.europa.eu/energy/nuclear/radioprotection/publication_en.htm
36
2. Radiation-induced genetic risk and non-cancer diseases
• Ionizing radiation, genetic risks and radiological protection: K. Sankaranarayanan
• New data on genetic risk : J. Angulo
• Radiation-induced cataracts: new evidence:
N. Kleiman
Although many improvements were made by ICRP in comparison with the previous draft, a number of important issues continued being of concern, the majority of which being in relation with insuffi cient application of the precautionary principle in view of new scientifi c evidence.
The mains issues discussed during this seminar are developed hereafter. It is important to note that these issues are still of concern in the fi nal text of the ICRP Recommendations, published in 2007 (ICRP Publication 103), as the main Commission of ICRP has maintained its value judgments, just explaining more in detail their rationale.
Radiation-induced cataracts: new evidence
According to US specialist, N. Kleiman, present guidelines are based on the view that cataractogenesis is a deterministic event and requires a threshold radiation dose before lens opacities will develop. Yet, lens opacities occur in populations exposed to far lower doses of radiation than generally assumed to be cataractogenic. This can be seen in those undergoing CT scans (Klein, 1993), radiotherapy (Wilde, 1997; Hall, 1999), the astronaut pool (Cucinotta, 2001; Rastegar, 2002), atomic bomb survivors (Minamoto, 2004; Nakashima, 2006), residents of contaminated buildings (Chen, 2001) and the Chernobyl accident “liquidators” (Worgul, 2003, 2007). As an example, in the Ukrainian American Chernobyl Ocular Study (UACOS) established in 1996 to monitor the effects of radiation exposure on the eyes of Chernobyl clean-up workers, the data indicate that the threshold for radiation cataract is far lower than current guidelines imply. Even though most study subjects had not yet progressed to stage 2 cataract or greater, with accompanying visual loss, the evidence to date already points to a dose threshold no greater than 700 mGy with ongoing study likely to lower the threshold response in future years. For stage I
37 posterior subcapsular radiation cataracts, the maximum likelihood estimate of a dose threshold was 350 mGy. These fi ndings strongly indicate that the current ICRP guidelines following fractionated or prolonged exposures of a 5 Gy threshold for detecting opacities and 8 Gy for visual impairment (ICRP, 1991) are much too high. Even current ICRP occupational guidelines for exposure limits to the lens, currently 150 mGy/year, may need to be re-evaluated in light of the present fi ndings and any continued follow-up and presumed cataract progression in the Liquidator population.
“If, indeed, there is a threshold for cataracts, it may be as much as an order of magnitude lower than current guidelines permit.”
Always according to N. Kleiman, this conclusion is further supported by re-analysis of the atomic bomb cataract data 56 years after exposure (Nakashima, 2006; Neriishi, 2007) which, at its lower limit for statistical signifi cance, reported a zero dose threshold for cataract development. The fi ndings in the Liquidator population are also in agreement with those from experimental low-dose radiation cataract animal studies. Recent fi ndings demonstrate dose-related signifi cant lens opacifi cation after exposure of rats to as little as 100 mGy X-rays.
Moreover, new observations even are consistent with the absence of a dose threshold. Although the mechanism of radiation induced cataracts is not known precisely, genomic damage resulting in altered cell division, transcription and/or abnormal lens fi ber cell differentiation is now considered to be the salient injury, rather than cell killing. For this reason, the classifi cation of cataracts as a deterministic effect must be called into question. Several lines of evidence from experimental and epidemiologic studies strongly suggest a stochastic basis for radiation cataracts. Animal studies have shown that individuals that are haplo-insuffi cient for multiple genes involved in DNA damage repair and/or cell cycle checkpoint control may be more susceptible to the cataractogenic effects of ionizing radiation than wild-types. Atm, Brca1 and Rad9 heterozygotes demonstrate enhanced sensitivity to radiation-induced cataract formation. The roles of Atm, Rad9 and Brca1 in the cell cycle and during DNA repair are consistent with a genotoxic basis for radiation cataractogenesis. These fi ndings may have important implications for radiosensitive subsets of the human population and for the astronaut core.
Globally, new data from animal models and from exposed human populations suggest that lens opacities occur at doses far lower than
38
those generally assumed to be cataractogenic and some observations are even consistent with the possible absence of a dose threshold (genetic susceptibilities: Atm, Brca1 and Rad9 heterozygotes).
The cataract issue belongs to the key issues identifi ed by the Article 31 Group of experts as worth being transmitted to ICRP for careful consideration, with the message that ICRP should not postpone revisiting the relationship between the dose to the lens and the occurrence of cataracts and revisiting the protection system (for instance introducing lens dose constraints based on good practice).
Risk of in utero irradiation: new evidence
As regards protection during pregnancy, the EU Basic Safety Standards Directive states that the protection of the child to be born shall be comparable with that provided to for members of the public, with work conditions for the mother making unlikely that the dose to the child to be born will exceed 1 mSv during “at least the remainder of the pregnancy”
(i.e. from the day the pregnant woman has informed the undertaking of her condition).
To limit the dose to the embryo during the fi rst days of his existence, the former BSS Directive stated that the dose to the abdomen of women of reproductive capacity shall not exceed 13 mSv in a quarter. This kind of provision has now disappeared.
In practice thus, the “child to be born” has now the same dose limit as the members of the public (at least from the declaration of the pregnancy).
As it was the case for the approach of the genetic risk, the risk from in utero irradiation is currently regarded with more optimism, and threshold fi gures, like the emblematic 100 mSv numerical value, are frequently presented as the break-point criterion in situations like emergency planning, post-accidental relocations or medical post-accidental irradiations. This evolution was noteworthy in the various draft ICRP Recommendations issued for public consultation and is still present in the fi nal recommendations.
39 Nevertheless, these last years, a lot of new radiobiological and epidemiological data became available. An EC Scientifi c seminar was devoted to this issue in 2001.2
After irradiation during the pre-implantation period, generally considered as safe with regard to the radiation-induced risks, non lethal congenital malformations have been induced in animals, particularly (but not only) in those with a genetic predisposition to specifi c congenital malformations or with genetic disorders in the pathways of DNA-repair.
Moreover, during the zygote-stage (about 1 day), there could be no threshold dose for the radiation-induction of congenital malformations in genetically predisposed animal strains.
After irradiation during the organogenesis, more congenital malformations have also been induced in animals with genetic disorders. There are similarities with the effects of chemical agents.
In these cases, the cause of the congenital malformations may not be an increased loss of cells (classic deterministic effect) but rather the persistence of un-repaired or mis-repaired DNA-damaged cells (“teratogenically damaged cells”).
Now, in humans, the same genetic susceptibilities probably exist: there are indeed families showing clusters of spontaneous congenital malformation.
There are also in humans many genes implicated in the DNA-damage response and involved in the genetic susceptibility to cancer induction by irradiation; if the mechanisms are similar (persistence of mis-repaired DNA-damaged cells), it is plausible that human genotypes leading to cancer-proneness are also associated with a genetic susceptibility to the radiation-induction of congenital abnormalities (or more subtle tissue dysfunctions).
Due to genetic susceptibilities, there could then be for some individuals a higher risk of radiation-induced malformations (or dysfunctions) or lower thresholds (or even no threshold at day 1?) and this risk could also exist during the “safe” periods of pre- and early post-implantation (when women are not aware of being pregnant). Although frequently assumed to be low, the frequency of these individuals is not known.
2 Effects of in utero exposure to ionising radiation during the early phases of pregnancy: http://www.europa.eu.int/comm/energy/nuclear/radioprotection/
publication/131_en.htm
40
This raises doubts about the “defi nite” and generalized character of the 100 mSv threshold dose for lethal, developmental or other detrimental effects (other than cancer) after irradiation during the fi rst trimester of pregnancy, currently applied by many as a practical criterion: this could be an unjustifi ed simplifi cation.
On the basis of the precautionary principle, does this not require cautiousness in the medical fi eld, particularly for high dose examinations, including those performed during the pre/post implantation stage, in women not aware of being pregnant? The application of the ten-day rule (planning the non-urgent examination within the ten days following the beginning of the menstruation), whenever the abdominal dose could be signifi cant, would largely reduce these problems.
When looking at the potential implications of all these new data, a basic question is how much scientifi c evidence is needed before the scientifi c community feels it is necessary to apply the precautionary principle.
A related question is to know if the various stakeholders (besides the experts) would need the same amount of evidence before recommending precautionary action.
The pregnancy issue was also part of the key issues identifi ed by the Article 31 Group of experts as worth being transmitted to ICRP for careful consideration, with the message that “due to the uncertainties
The pregnancy issue was also part of the key issues identifi ed by the Article 31 Group of experts as worth being transmitted to ICRP for careful consideration, with the message that “due to the uncertainties