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Program of the 2000 Annual Meeting, Ionizing Radiation Science and
Protection in the 21st Century
April 5-6, 2000
General Introduction
S. James Adelstein & Warren K. Sinclair, Session Co-Chairs
The New Millennium: Values, Perceptions of Risk, and the Key Roles of Science and Technology
Gilbert S. Omenn, University of Michigan
What Views and What Uses of Radiation Sources in the 21st Century?
Hans Blix, International Atomic Energy Agency
Considering that in 1899 neither biotechnology nor the electronic revolution were foreseen, some humility might be advisable when one looks into the crystal ball for the future role of radiation sources. In the past 50 y nuclear medicine, nuclear weapons, and nuclear power have had a huge impact in the world. In the next 50 y nuclear weapons may be phased out, nuclear power revived, and nuclear medicine may continue, especially for diagnostic purposes. Conflicts between great powers and blocks will no longer be about territorial or ideological domination but about trade, finance, information and the environment and the weapons used will not be bombs but investments, credits and control of information. Nuclear power—still based on fission— will be relaunched and get more uses, e.g., to propel ships, to produce heat for industry and for space heating, and perhaps to desalinate water. The public will be more at ease with radiation as it is better educated, as nuclear safety continuously improves and new types of nuclear power plants emerge, as waste sites fail to cause any problems, and as no other energy source is found to deliver so much energy at reasonable cost with negligible impact on climate and environment. 1 kg of oil corresponds to 4 kWh of electricity. 1 kg of uranium fuel corresponds to 50,000 kWh, and 1 kg of plutonium 6,000,000 kWh! In nuclear medicine, radiation may give way to other treatments as the understanding of cancer advances. On the other hand, the extreme ease with which sources of radiation can be identified is unmatched and likely to make them useful tools as tracers and markers in medicine—and other fields—for a long time. For certain uses—perhaps food irradiation—radiation sources, like cobalt, may be replaced by accelerators which may be switched on and off at will. As more sources are used, registration and control of them must be made very effective around the whole world. Very high emissions of radon will continue to call for cautionary measures, but many other nonradiating substances will be identified as hazardous to health and call for vigorous intervention.
Scientific Basis for Radiation Protection in the 21st Century
R. Julian Preston, Session Chair
Deterministic Effects
R.J. Michael Fry, Oak Ridge, Tennessee
Deterministic effects are distinguished from stochastic effects for radiation protection purposes by the following characteristics: both incidence and severity increase as a function of dose after a threshold dose is reached. Cell killing is central to all deterministic effects with the exception of radiation-induced cataracts. The understanding of radiation-induced killing of cells has increased greatly in the last decade with an extraordinarily intense interest in apoptosis. Programmed cell death has long been known to developmental biologists and the importance of cell death has been recognized and quantified by tumor biologists and students of cell kinetics but the coining of a new name and the increase of understanding of the molecular aspects of cell death has stimulated interest. Some cells appear to be very sensitive to radiation and undergo apoptosis whereas, others such as fibroblasts do not with equal frequency. This characteristic, like many others, underlines the genetic differences among cell types. We are reaching a time that there are techniques and the knowledge to apply them to clinical and radiation protection problems. In radiotherapy, success depends on the differential effect between tumor and normal tissues that is obtained. To design the optimum therapy a profile of both the tumor cells and the cells of the normal tissues that may be at risk would help. The profile would characterize the radiosensitivity and the underlying factors which could help in the choice of adjunct therapy for tumor and normal tissue. Fibrosis, a common unwanted late effect, appears to be influenced by genetic factors, at least in experimental animals. The techniques are available for treating people as individuals more than ever before and that must be a good thing to do. Protection against deterministic effects would seem an easy matter but we are uncomfortably ignorant of the precise effect of protracted low-dose irradiation on tissues, such as the bone marrow and the testis, important features of risk in space. Entering the new century, it may be timely to classify radiation effects, as RERF has done, into cancer, genetic effects, and noncancer effects. The recognition in the atomic-bomb survivors of noncancer effects at doses in the order of 0.5 Sv (half the dose level considered a threshold in earlier studies) should stimulate interest in deterministic effects.
Resolving the Molecular Mechanisms of Radiation Tumorigenesis: Past Problems and Future Prospects
Roger Cox, National Radiation Protection Board,
United Kingdom
In a radiological protection context, studies on the molecular mechanisms of radiation tumorigenesis generally seek to forge links between cellular radiobiology and epidemiology. In essence, such linkage can make more secure some important scientific judgments regarding tumorigenic risk. Amongst these judgements, dose/dose rate effects, the influence of radiation quality and the role of heritable factors will continue to demand close research attention in the early years of this millennium. Technical and academic developments in cancer biology/genetics and genome research over the last decade have provided the means to closely associate mechanisms of DNA damage response/mutagenesis with those of radiation tumorigenesis. In an often related fashion it has proved possible to approach fundamental aspects of genetic- environmental interactions in the context of radiation risk. A particularly productive area of current research involves the coupling of animal sciences with molecular genetics. This research in model systems is beginning to provide information on initiating mutations in target genes, on the features of subsequent multistage tumor development and on the germ line loci that influence tumor specificity/multiplicity. Doubtless, these approaches with model rodent systems will continue to be most productive over the next 10 y and, for the linkage sought, we should also expect much new information on the molecular/biochemical aspects of early post-irradiation cellular response. However, as well as being challenged with a cascade of new information (e.g., via DNA chip technologies) we will increasingly face the question of how realistic it is to extrapolate complex experimental data sets to cancer risk in humans – “proof of principle” evidence is very valuable but, often, not sufficient. Here, the future problem is not one of technical insufficiency for the direct study of relevant human material but rather its availability. Potential target genes in a range of radiation-associated human tumors can and have been analyzed; work is also underway on potentially relevant human germ line gene polymorphisms. However, in order to promote this important area of future study it is essential that dialogue/interaction between interested parties is coordinated and that there is careful audit of available human material/study groups – fragmentation of effort is probably the greatest danger. A personal projection to 2010 would place genetic susceptibility to cancer and knowledge of patterns of individual risk as the area of greatest growth. The linear nonthreshold dose response debate seems likely to continue and, for tumorigenic responses at a few tens of millisievert, weight of evidence arguments incorporating increasing volumes of complex data may not become easier – wholly decisive data sets are likely to be elusive beasts.
Radiation Risk Estimates in the 21st Century
Elisabeth Cardis, International Agency for Research on Cancer, France
In the early years of the 21st century, results from a number of epidemiologic studies of populations with specific exposures will become available. These include populations with accidental exposures in the former USSR and elsewhere, populations with occupational and environmental exposures from routine operations of nuclear power plants, populations with environmental exposures to natural sources of radiation such as radon. It is unlikely that any of these populations will replace those of the atomic-bomb survivors and the miners as a central basis for the estimation of radiation risks. Many of these studies, however, will provide specific information to complement the atomic-bomb survivor studies, particularly the effects of dose rate and exposure protraction, modifiers of radiation risks (both environmental and host factors) and different types of radiation. These studies will, therefore, be important as a test of the adequacy of the assumptions made to extrapolate risks from the atomic-bomb survivor and miner data to the circumstances of exposure and the population groups of interest for the protection of workers and the general public. An example is thyroid cancer risk in young children following the Chernobyl accident, which has brought attention to a very high sensitivity of very young children which was difficult to assess on the basis of atomic-bomb data alone. It is likely that the use of biologically based models for risk estimation will become more common and that attempts will be made to analyse jointly data from different epidemiological studies using a Bayesian approach. Information for the development of the risk models may come both from experimental studies and from comparisons of epidemiological studies with different exposure circumstances and different population characteristics. Although tremendous advances have been made recently in the cellular and molecular biology and genetics of radiation carcinogenesis, much of this work is carried out at doses and dose rates which are considerably higher than those of interest for radiation protection. It is unclear, therefore, whether sufficient information will be available from experimental work to assist in the determination of low-dose radiation risks in the foreseeable future.
Scientific Basis for Radiation Protection in the 21st Century (continued)
Ethel S. Gilbert, Session Chair
The Future of Cancer Control
Robert Hoover, National Cancer Institute
A common, overly simplistic, but useful model of disease control incorporates the concepts of primary prevention, early detection, treatment and rehabilitation. Control over categories of diseases is usually achieved by the complementary and often overlapping implementation of effective interventions in each of these areas. While such interventions can be and have been discovered through empiricism or good fortune, the pace at which such discoveries are made is directly related to the level of understanding of the mechanisms of disease causation. The most illustrative example of this is in the area of infectious diseases. Some effective preventions and treatments were developed over several millennia, but true control was only rapidly and effectively achieved in the past 150 y following the establishment of the microbial nature of these diseases and the resultant unraveling of their presence and mechanisms of action. Currently, there is high enthusiasm that the revolution in genetic and molecular science and technology within the last 15 y has brought us to the analogous point for cancer, and that breakthroughs in prevention, early detection and treatment will dominate the next several decades, leading to truly effective cancer control early in the 21st century. NCI and private sector initiatives in research and development have clearly shifted to pervasive incorporation of molecular science into identification of cancer causes, host susceptibility, early markers, and selective therapeutics. While the promise of unprecedented progress is high, the difficulties in achieving this are many and daunting, and largely underappreciated. Examples of both the promise and the difficulties of these new approaches are beginning to appear, often simultaneously within the same issue. Effective meeting of the challenges and mining of the opportunities is likely to require new research paradigms and infrastructures focused in these areas.
Estimation of the Hereditary Risks of Exposure to Ionizing Radiation: History, Current Status, and Emerging Perspectives
K. Sankaranarayanan, Sylvius Laboratories, The Netherlands
Serious concern over the adverse hereditary (genetic) consequences of exposure to ionizing radiation came to the forefront of attention in the aftermath of World War II. In the ensuing five decades, the field of genetic risk estimation has evolved. Up to about the mid-1980s, this evolution was driven chiefly by advances in mouse radiation genetic studies. Starting in the early 1990s, advances in human genome research began to be incorporated into the conceptual framework of genetic risk estimation. The goal of genetic risk estimation is to predict the risk of inducible genetic diseases in the descendants of a population exposed to radiation using the frequencies of naturally-occurring diseases in the population (i.e., in the absence of radiation) as a baseline.The prediction is made using the so called “doubling dose method” the general concept of which is summarized in the equation:
Risk per unit dose = P x [1/DD] x MC
where P is the incidence of the disease class under study (i.e., the three sub-classes: Mendelian diseases, congenital abnormalities, and chronic multifactorial diseases), 1/DD is the relative mutation risk per unit dose [obtained by first calculating a doubling dose (DD) as a ratio of spontaneous and induced mutation rates in a set of genes and taking the reciprocal] and mutation component (MC) is a measure of how the disease frequencies will increase with an increase in mutation rate. MC is disease-class specific. Advances during the last decade include (1) revision of the baseline frequencies of Mendelian diseases, (2) revision of the conceptual basis and magnitude of the DD, (3) development of methods to estimate MC for the different classes of genetic diseases, (4) bridging the gap between mouse data on radiation-induced mutations and the risk of induced genetic disease in humans, (5) reconciliation of the results of the genetic studies carried out on atomic-bomb survivors in Japan with the risks predicted using the DD method, and (6) the hypothesis (and supporting evidence) that the main adverse genetic effects of radiation will be reflected as multisystem developmental abnormalities. It is now clear that in the coming decade, advances in risk estimation will be intimately linked to those in human genome research. When the structural genomic maps are completed, and functional genomic maps are constructed, we will have the unprecedented opportunity to analyse genomic region by genomic region and ask whether induced genetic damage in a given region can be compatible with survival (and thus recoverable in live births) and then carry out studies in model organisms such as the mouse to gain insights into their potential phenotypes in humans.
Developing Public Policy in the 21st Century
Susan D. Wiltshire, Session Chair
Public Involvement in Science and Decision Making
John E. Till, Risk Assessment Corporation
Members of the public are becoming increasingly interested in understanding risks associated with their exposure to radionuclides and chemicals in the environment. They also want to be more involved in decision making about future exposures to risks. This paper reviews a community’s involvement in decisions about technical methods employed and cleanup criteria for the Rocky Flats Environmental Technology Site near Denver, Colorado. It is anticipated that much of the site will be available for public use following cleanup. After considerable public concern was expressed about proposed cleanup standards for the site in 1996, a community panel was established by the U.S. Department of Energy to oversee an independent calculation of radionuclide soil action levels that will be used as the basis for cleanup at Rocky Flats. The primary radionuclides of concern were 239+240Pu. The panel was substantively involved in all aspects of the work, from selecting a computer code that formed the basis of the calculation to deciding upon values for the approximately 100 input parameters that were ultimately used. Uncertainties were included in the analysis of soil action levels that presented a particularly unique challenge from the public’s perspective. Over the course of the 18 month project, the community panel gained an understanding and appreciation of the technical elements of the calculation and the sensitivities of the different parameters. The panel recommended the technical approach that will be the basis for proposing soil action levels for cleanup of the site to the U.S. Department of Energy. This project serves as a model of the future for effectiveness of public involvement in science and decision making. It also illustrates the difficulties and expectations of working with stakeholders to make decisions. Although the process was tedious and time consuming for the scientists responsible for the calculations, a more defensible and better-supported soil action level emerged in the end.
(Re)Building Trust in Established Institutions
James P. Thomas, Short, Cressman & Burgess, PLLC
The established institutions responsible for the setting and enforcement of radiation protection standards are facing increased demands from the public to be more accountable. In the past, the NCRP and others within the radiation protection community have relied chiefly on professional relationships to build trust among government agencies, health care providers, and industry. During the last four decades, the trust of the public in society's institutions has eroded significantly. This diminishment of faith in recognized experts and the unparalleled characteristics of the production, testing and use of nuclear weapons pose a serious challenge to those within the radiation protection establishment. When other factors such as the limits of scientific knowledge are considered, the issue of trust takes on immense proportions. This presentation will explore how radiation standard-setters and regulators can build trust by respecting the demands of a skeptical populace for meaningful participation in the decision-making process.
Scientists, Policy Makers, and the Public: A Needed Dialogue
John F. Ahearne, Sigma Xi
Effective incorporation of scientific knowledge into public policy requires effective dialogue among scientists, policy makers, and the general public. How can this be accomplished so that all three groups have confidence in the processes leading to policies? What are the appropriate roles for scientists? What are the appropriate uses of science? Suggested answers will be proposed.
Twenty-Fourth Lauriston S. Taylor Lecture on Radiation Protection and Measurements
Introduction of the Lecturer, Barbara J. McNeil
Administered Radioactivity: Unde Venimus Quoque Imus, S. James Adelstein
Risk Management and Standards in the 21st Century
Michael T. Ryan, Session Chair
Harmonizing Controls for Chemicals and Radionuclides
U.S. Environmental Protection Agency
Can Radiation and Chemical Risk Management be Harmonized?
Paul Locke & Nga Tran, Johns Hopkins School of Hygiene and Public Health
One of the most important challenges facing risk mangers in the coming decades is the joint management of chemical and radiological wastes. Born out of different traditions, radiation and chemical risk approaches can differ sharply. Radiation protection generally focuses on establishing effective dose levels across media and utilizes an approach that incorporates the philosophy of ALARA. In contrast, chemical risk management strategies are medium specific and risk based. In practice these differences can complicate decision making and potentially lead to duplicative efforts.
We have undertaken a series of case studies to determine the extent and nature of the barriers that exist with regard to the potential harmonization of risk management approaches. Built upon the results of an interactive workshop held in June 1998, these case studies examine how cleanup decisions were made at a series of contaminated sites around the United States. It is anticipated that these case studies will demonstrate (1) the areas of greatest discord among chemical and radiological risk management approaches, and (2) how gaps in approaches could be bridged.
This presentation will review the important conclusions of these case studies and (if possible) offer suggestions about how chemical and radiation risk management can be harmonized.
Control of Low-Level Radiation Exposure: Time for a Change?
Roger H. Clarke, National Radiation Protection Board,
United Kingdom
The carcinogenic risks of exposure to low-level ionizing radiation used by ICRP have been challenged as being, at the same time, both too high and too low. This paper explains that the epidemiological evidence will always be limited at low doses, so that understanding the cellular mechanisms of carcinogenesis is increasingly important to assess the biological risks. An analysis is then given of the reasons why the challenges to ICRP, especially about the linear nonthreshold response model, have arisen. As a result of considering the issues, the Main Commission of the ICRP is now proposing a revised, simpler approach based on the concept of what is being called “controllable dose.” This is an individual based philosophy and represents a shift in emphasis by the Commission from societal-oriented criteria using collective dose. Finally the paper speculates on the consequences for radiological protection of such a change in policy. The Commission wishes its ideas to be discussed as part of its reconsideration of its recommendations.
Alternative Goals and Policy Mechanisms for Radiation Protection
H. Keith Florig, Carnegie Mellon University
As laid out in NCRP Report No. 116, NCRP's current radiation protection guidelines are based on three principles: (1) that the societal benefits of the exposure-producing activity exceed its social costs; (2) that radiation risks be reduced to as low as reasonably achievable (ALARA), accounting for economic and social factors; and (3) that no individual or group should be exposed to risks exceeding those that are “acceptable.” NCRP provides little guidance on how the first of these principles might be operationalized, but NCRP exposure standards serve as bright lines for acceptable risk, and NCRP advocacy of the ALARA principle has resulted in actual radiation exposures that are significantly below NCRP standards. This paper addresses several questions raised by the status quo: (1) are NCRP's three principles of radiation protection complete, (2) what are the sources of ambiguity in applying these principles and how can their application be made more systematic and consistent across the various domains of radiation protection, and (3) what policy mechanisms other than exposure standards might be used to implement these principles?
The NCRP in the 21st Century
Charles B. Meinhold, National Council on Radiation Protection and Measurements
The Program Committee
S. James Adelstein, Co-Chair
Warren K. Sinclair, Co-Chair
Ethel S. Gilbert
R. Julian Preston
Michael T. Ryan
John E. Till
Susan D. Wiltshire
Telephone: 1-800-229-2652, Ext. 25
Email: NCRPpubs@NCRPonline.org
Fax: 301-907-8768
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