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Biomedical subjects

D C Kocher

Publications and source records attributed to D C Kocher.

At least 19 recordsLinked to original sources
PubMed2005

Radiation effectiveness factors for use in calculating probability of causation of radiogenic cancers.

This paper presents so-called radiation effectiveness factors that are intended to represent the biological effectiveness of different radiation types, relative to high-energy Co gamma rays, for the purpose of estimating cancer risks and probability of causation of radiogenic cancers in identified individuals. Radiation effectiveness factors are expressed as subjective probability distributions to represent uncertainty that arises from uncertainties in estimates of relative biological effectiveness obtained from radiobiological studies of stochastic endpoints, limited data on biological effectiveness obtained from human epidemiological studies, and other judgments involved in evaluating the applicability of available information to induction of cancers in humans. Primarily on the basis of reviews and evaluations of available data by experts, probability distributions of radiation effectiveness factors are developed for the following radiation types: neutrons of energy less than 10 keV, 10-100 keV, 0.1-2 MeV (including fission neutrons), 2-20 MeV, and greater than 20 MeV; alpha particles of any energy emitted by radionuclides; photons of energy 30-250 keV and less than 30 keV; and electrons of energy less than 15 keV. Photons of energy greater than 250 keV and electrons of energy greater than 15 keV are assumed to have the same biological effectiveness as reference Co gamma rays and are assigned a radiation effectiveness factor of unity, without uncertainty. For neutrons and alpha particles, separate probability distributions of radiation effectiveness factors are developed for solid tumors and leukemias, and small corrections to represent an inverse dose-rate effect are applied to those distributions in cases of chronic exposure. A radiation effectiveness factor different from unity for 15-60 keV electrons is discussed but is not adopted due to a lack of relevant radiobiological data. Radiation effectiveness factors presented in this paper are incorporated in the Interactive RadioEpidemiological Program and were developed for use by The National Institute for Occupational Safety and Health and U.S. Department of Labor in evaluating claims for compensation for radiogenic cancers by workers at U.S. Department of Energy facilities.

Algorithms↗
PubMed2002

An approach to comparative assessments of potential health risks from exposure to radionuclides and hazardous chemicals.

The need to compare potential health risks to the public associated with different activities that can result in releases of hazardous substances to the environment is becoming increasingly important in decision-making. In making such comparisons, it is desirable to use equivalent indicators of potential health risks for radionuclides, chemical carcinogens, and noncarcinogenic hazardous chemicals. Current approaches to risk assessment that were developed for purposes of protecting human health do not provide equivalent indicators of potential risks from exposure to radionuclides and hazardous chemicals. Comparisons of environmental concentrations or calculated exposures or risks with standards for protection of public health also do not provide equivalent indicators of potential risks. We propose a simple approach to comparative risk assessments in which calculated exposures to any hazardous substances are expressed relative to no-observed-effect levels (NOELs) or, preferably, lower confidence limits of benchmark doses (BMDLs) in humans. This approach provides an equivalent, science-based indicator of the relative risks posed by different exposures to any hazardous substances.

Benchmarking↗
PubMed2001

Drinking water standards for radionuclides: the dilemma and a possible resolution.

The U.S. Environmental Protection Agency (EPA) is undertaking a revision of existing standards for radionuclides in drinking water. The Safe Drinking Water Act specifies that any revision "shall maintain or provide for greater protection of the health of persons." This provision appears to require that existing standards (maximum contaminant levels, MCLs) cannot be relaxed. Such a requirement presents a dilemma for two reasons. First, EPA has shown that the MCL for radium was not cost-effective. Second, MCLs for beta/gamma-emitting radionuclides incorporate outdated approaches to estimating dose from ingestion of radionuclides and, thus, appear to violate provisions of the Safe Drinking Water Act concerning the use of sound science in setting standards. We suggest that this dilemma can be resolved based on an argument that the standard for protection of public health mandated by the Safe Drinking Water Act is one of applying best-available technology for removal of contaminants from drinking water at a reasonable cost, not one of meeting previously established MCLs.

Humans↗
PubMed2000

On the application of a radiation weighting factor for alpha particles in protection of non-human biota.

Radiation protection standards for non-human biota have been expressed in terms of absorbed dose. In calculating dose to biota, some investigators have modified the absorbed dose due to alpha particles by a factor of 20, based on the radiation weighting factor used in protection of humans, to account for the greater effectiveness of these radiations in producing biological damage. However, this value is intended to apply to stochastic health effects, primarily cancers, whereas deterministic effects have been the primary concern in protection of biota. Based on an analysis by the International Commission on Radiological Protection, the deterministic radiation weighting factor for alpha particles appears to lie in the range of about 5-10. Given the potential importance of this weighting factor in determining allowable levels of alpha-emitting radionuclides in the environment, regulatory authorities must be impressed with the need to develop an appropriate value for use in protection of biota. There also is a need to express doses and dose limits for biota in terms of a quantity other than absorbed dose and to develop an appropriate name for the biologically significant dose to biota.

Alpha Particles↗
PubMed1991

A validation test of a model for long-term retention of (129)I in surface soils.

A linear compartment model for global transport of iodine that we previously developed predicted that the mean residence time of iodine in the first 1 m of surface soil is about 4,000 y. An independent test of the model prediction is provided by measured depth profiles of (129)I in soil following atmospheric releases from the Savannah River Plant (SRP) in South Carolina and from the Karlsruhe fuel reprocessing plant in Germany. Previous analyses of these data using a linear compartment model for downward transport through soil indicated that the mean residence time in the first 0.3 m is about 40 y at both locations, which suggests that removal of (129)I from surface soil may be considerably more rapid than predicted by the global transport model. In this paper, a diffusion model is used to describe the measured soil profiles of (129)I at Savannah River. The diffusion coefficient obtained from the analysis corresponds to a mean residence time in the first 1 m of surface soil that agrees semi-quantitatively with the prediction of the global model when the concentration of naturally occurring stable iodine in soil and the flux of iodine from the atmosphere onto surface soil at Savannah River, as they differ from globally averaged values, are considered. This paper also discusses (1) the importance of the mean residence time of (129)I in surface soil for estimates of dose to individuals from near-surface land disposal of low-level radioactive wastes and (2) unresolved issues regarding global cycling of iodine.

Diffusion↗
PubMed1991

Perspective on the historical development of radiation standards.

This paper discusses the historical development of standards for limiting routine radiation exposures of workers and the public. The radiobiological and epidemiological basis for radiation protection standards and practices, as this basis has evolved over time, is emphasized. Difficulties with using dose equivalents and nominal risk factors, which were developed primarily for purposes of radiation protection (i.e., to establish dose limits), in estimating radiation risks at the low levels of exposure routinely experienced in the workplace and the environment are discussed. The increasing importance of the principle that exposures should be reduced as low as reasonably achievable (ALARA) in radiation protection of workers and the public is described.

History, 20th Century↗
PubMed1989

Relationship between kidney burden and radiation dose from chronic ingestion of U: implications for radiation standards for the public.

Metabolic models for U in adults recommended by Wrenn et al. (1985) and the International Commission on Radiological Protection (ICRP 1979a) were used to study the relationship between kidney burden and radiation dose from chronic ingestion of soluble 238U or natural U and whether current radiation standards for the public provide adequate protection against chemical toxicity from U in the kidney. We assumed that the threshold concentration for chemical toxicity is 1 microgram of U g-1 of kidney and that a safety factor of 10 should be applied in limiting kidney burdens for maximally exposed individuals in the general public. We found that a limit on annual effective dose equivalent of 1 mSv (0.1 rem) for chronic exposures of the public from all sources, as recommended by the ICRP (1985) and the National Council on Radiation Protection and Measurements (NCRP 1987), corresponds to concentrations of U in the kidney from chronic ingestion that exceed the assumed threshold for chemical toxicity of 1 microgram g-1 only for 238U using the metabolic model of the ICRP (1979a). However, using either metabolic model (ICRP 1979a; Wrenn et al. 1985), the predicted concentrations of U in the kidney exceeded the limit of 0.1 microgram g-1, based on the assumed safety factor for protection of the public, for both 238U and natural U. From these results, we concluded that chemical toxicity should be considered in developing health protection standards for the public for ingestion of soluble 238U or natural U. Environmental radiation standards for certain practices established by the U.S. Environmental Protection Agency and Nuclear Regulatory Commission (EPA 1987a, 1987b, 1987c, 1987d; NRC 1988a) are consistent with a limit on annual effective dose equivalent of 0.25 mSv (25 mrem) per practice. If the metabolic model of Wrenn et al. (1985) is assumed to be appropriate for chronic ingestion of soluble U in the environment, then the dose limit of 0.25 mSv corresponds to a concentration of 238U or natural U in the kidney that is below the assumed limit of 0.1 microgram g-1 for members of the public. Inhalation of soluble and insoluble U and ingestion of insoluble U were considered. Except for inhalation of soluble U, these modes of intake reduced predicted concentrations in the kidney per unit effective dose equivalent compared with values for ingestion of soluble U. Unresolved issues of importance for determining the significance of chemical toxicity relative to radiation dose in establishing limits on public exposures for U also are discussed.

Adult↗
PubMed1988

On the relationship between radiation standards for the general public and limitation of lifetime risk.

This paper discusses the relationship between standards for limiting radiation exposures of individuals in the general public and limitation of lifetime risk. Most current radiation standards for the public in the United States specify limits on dose for each year of exposure. Particularly for internal exposures, we show that such standards may correspond poorly with a limit on lifetime risk when the age dependence of radionuclide intakes and dose is taken into account. We then show that standards which specify limits on annual dose averaged over a lifetime, with a subsidiary limit on dose in any year, correspond more closely with a limit on lifetime risk. Finally, we discuss standards for public exposures that are expressed directly as limits on lifetime risk. The development of risk standards would require consideration of age-dependent radiogenic risks and competing risks from all other causes as well as age-dependent dosimetry. We present sample calculations of lifetime risks from acute and chronic intakes that would support such a standard. We suggest that implementation of a standard for lifetime risk would require modification or abandonment of several radiation protection practices embodied in standards which specify limits on dose.

Adolescent↗
PubMed1987

A proposal for a generally applicable de minimis dose.

This paper presents a proposal for a generally applicable de minimis radiation dose for members of the general public. A de minimis dose defines a level below which control of radiation exposures would be deliberately and specifically curtailed. Thus, such a dose must be set well below established limits on acceptable dose from all sources of exposure and, furthermore, must be below any established dose limit for specific practices. The proposed de minimis level consists of two dose limits: a principal limit on annual committed effective dose equivalent averaged over a lifetime of 0.01 mSv (1 mrem) and a subsidiary limit on committed effective dose equivalent in any year of 0.05 mSv (5 mrem). The proposed values are 1% of the limits on acceptable dose from all sources currently recommended by the International Commission on Radiological Protection (ICRP85), and correspond to a lifetime risk from continuous exposure of about 10(-5).

Cost-Benefit Analysis↗
PubMed1987

Electron dose-rate conversion factors for external exposure of the skin from uniformly deposited activity on the body surface.

Dose-rate conversion factors have been calculated for external exposure of the skin from electrons emitted by sources that are deposited uniformly on the body surface. The dose-rate factors are obtained from electron scaled point kernels developed by Berger (Be71; Be73; Be74). The dose-rate factors are calculated at depths of 4, 8, and 40 mg cm-2 below the body surface as recommended by Whitton (Wh73), and at a depth of 7 mg cm-2 as recommended in ICRP Publication 26 (ICRP77). The dependence of the dose-rate factors at selected depths on the energy of the emitted electrons is displayed. The dose-rate factors for selected radionuclides of potential importance in radiological assessments are tabulated.

Beta Particles↗
PubMed1987

Sensitivity and uncertainty studies of the CRAC2 computer code.

We have studied the sensitivity of health impacts from nuclear reactor accidents, as predicted by the CRAC2 computer code, to the following sources of uncertainty: (1) the model for plume rise, (2) the model for wet deposition, (3) the meteorological bin-sampling procedure for selecting weather sequences with rain, (4) the dose conversion factors for inhalation as affected by uncertainties in the particle size of the carrier aerosol and the clearance rates of radionuclides from the respiratory tract, (5) the weathering half-time for external ground-surface exposure, and (6) the transfer coefficients for terrestrial foodchain pathways. Predicted health impacts usually showed little sensitivity to use of an alternative plume-rise model or a modified rain-bin structure in bin-sampling. Health impacts often were quite sensitive to use of an alternative wet-deposition model in single-trial runs with rain during plume passage, but were less sensitive to the model in bin-sampling runs. Uncertainties in the inhalation dose conversion factors had important effects on early injuries in single-trial runs. Latent cancer fatalities were moderately sensitive to uncertainties in the weathering half-time for ground-surface exposure, but showed little sensitivity to the transfer coefficients for terrestrial foodchain pathways. Sensitivities of CRAC2 predictions to uncertainties in the models and parameters also depended on the magnitude of the source term, and some of the effects on early health effects were comparable to those that were due only to selection of different sets of weather sequences in bin-sampling.

Accidents↗
PubMed1985

Dose-rate conversion factors for external exposure to photon emitters in soil.

Dose-rate conversion factors have been calculated for external exposure above ground to monoenergetic photon emitters in soil. These factors give external dose rates per unit source concentration in soil. The calculations are based on the point-kernel integration method and assume that the source concentration at any depth in soil is uniform over an infinite surface parallel to the ground plane. Dose-rate factors in air at a height of 1 m above ground are tabulated for discrete photon energies between 0.01 and 10 MeV and for source depths in soil between 0 and 300 cm. Application of the results for plane sources in soil to the calculation of photon dose rates from distributions of sources with depth in soil is described, and dose-rate factors are tabulated for the particular cases of uniform slab sources of finite thickness and sources which are exponentially distributed with depth. We also demonstrate how dose-rate factors in air for monoenergetic photon sources are used to estimate dose-rate factors for body organs of exposed individuals and for the spectrum of photons from radioactive decay. The calculations in this paper show that allowing for downward migration of radionuclides in soil can result in significant reductions in external dose compared with the usual assumption that radionuclides which are deposited on the ground surface remain there until removal by radioactive decay.

Environmental Exposure↗
PubMed1983

Dose-rate conversion factors for external exposure to photons and electrons.

Dose-rate conversion factors for external exposure to photons and electrons have been calculated for approx. 500 radionuclides of potential importance in environmental radiological assessments. The three exposure modes considered are immersion in contaminated air, immersion in contaminated water, and irradiation at a height of 1 m above a contaminated ground surface. For each exposure mode, the source region is assumed to be effectively semi-infinite or infinite in extent with uniform radionuclide concentration. The dose-rate factors then give external dose-equivalent rates per unit radionuclide concentration in air, in water or on the ground surface. The results are tabulated in this paper in the form of effective dose-rate factors based on the definition of the effective dose equivalent given in ICRP Publication 26 (ICRP77). The effective dose-rate factors are obtained from photon dose-rate factors for 23 separate body organs and electron dose-rate factors for skin calculated with the revised DOSFACTER computer code (Ko81a). In addition to presenting the dose-rate factor equations and the tabulated results, this paper emphasizes the assumptions underlying the calculations for each exposure mode, differences between the organ dose-rate factors for photons used here and those used previously with the original version of the DOSFACTER code (Ko80a), and limitations inherent in application of the idealized external dose-rate factors to realistic environmental radiological assessments.

Air Pollutants↗