47 research outputs found
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Aspects of the dosimetry of radionuclides within the skeleton with particular emphasis on the active marrow
Epidemiological surveys on man and results from animal experiments have shown that two tissues associated with the skeleton are of primary concern with respect to cancer induction by ionizing radiation. These are the cells on or near endosteal surfaces of bone, from which osteosarcomas are thought to arise, and hematopoietic bone marrow, which is associated with leukemia. The complex geometry of the soft tissue-bone intermixture makes calculations of absorbed dose to these target regions a difficult problem. In the case of photon or neutron radiations, charged particle equilibrium may not exist in the vicinity of soft tissue-bone mineral interface. In this paper a general study of the dosimetry of radionuclides within the skeleton is presented. Dosimetric data consistent with the MIRD schema and reflecting the physical and anatomical parameters defining the energy deposition are tabulated for the relevant target regions. 27 refs., 5 figs., 5 tabs
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Dosimetric methodology of the ICRP
Establishment of guidance for the protection of workers and members of the public from radiation exposures necessitates estimation of the radiation dose to tissues of the body at risk. The dosimetric methodology formulated by the International Commission on Radiological Protection (ICRP) is intended to be responsive to this need. While developed for radiation protection, elements of the methodology are often applied in addressing other radiation issues; e.g., risk assessment. This chapter provides an overview of the methodology, discusses its recent extension to age-dependent considerations, and illustrates specific aspects of the methodology through a number of numerical examples
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Impact of risk considerations on dosimetry of radiopharmaceuticals
Estimates of the absorbed dose from clinical procedures involving the administration of radiopharmaceuticals are used primarily to determine the presumed risk of various procedures so that, in-so-far as possible, the selection of a given procedure can be based on a comparison of risk. Although this has been the basic objective, risk evaluation has generally been separated from the dosimetry considerations. In the recent revision of its radiation protection guidance, the International Commission on Radiological Protection (ICRP) has embodied risk considerations in its recommendations and risk concepts have become an integral part of the dosimetric framework. The impact of these considerations on the dosimetric assessments of radiopharmaceuticals and the resulting need for additional information is discussed
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Recommended ALIs and DACs for 10 CFR part 220: A consistent numerical set
Appendix B to 10 CFR Part 20 contains numerical data for controlling the intake of radionuclides in the workplace or in the environment. These data, derived from the recommendations of the International Commission on Radiological Protection (ICRP), do not provide a numerically consistent basis for demonstrating compliance with the limitation on dose stated in the regulation. This situation is largely a consequence of the numerical procedures used by the ICRP which did not maintain, in a strict numerical sense, the hierarchial relationship among the radiation protection quantities. In this work recommended values of the quantities in Appendix B to CFR Part 20 are developed using the dose coefficients of the applicable ICRP publications and a numerical procedure which ensures that the tabulated quantities are numerically consistent
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Conversational eigenanalysis program for solving differential equations
Dynamic models that arise in health physics applications are often expressed in terms of systems of ordinary differential equations. In many cases, such as box models that describe material exchange among reservoirs, the differential equations are linear with constant coefficients, and the analysis can be reduced to the examination of solutions of initial-value problems for such systems. This paper describes a conversational code, DIFSOL, that permits the user to specify the coefficient matrix and an initial vector of the system; DIFSOL prints out closed-form solutions (i.e., expressed as linear combinations of terms of the form e/sup -at/, e/sup -at/cos bt, and e/sup -at/sin bt) and tables of the solution, its derivative, and its integral for any specified linear combination of state variables. The program logic permits menu-driven control. We have operated a FORTRAN IV version of the code on a DEC PDP-10 for several years. A translation into BASIC has proved practical on Radio Shack TRS-80 Model I and III personal computers for smaller systems of differential equations (< 12 state variables). The paper includes illustrations of the use of DIFSOL in studying metabolic models
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DOSEXPRT: A bioassay dosimetry code for Martin Marietta Energy Systems, Inc
The bioassay code DOSEXPRT was developed for Martin Marietta Energy Systems, Inc., to provide compliance with Department of Energy (DOE) Order 5480, Chapter 11. DOSEXPRT computes the intake of a radionuclide in any year (considering both acute and chronic intakes) from in vivo measurements of the retained activity and/or measurements of the activity in excreta. The committed effective and organ doses for the intake are computed as well as the effective and organ doses expected to be received in each calendar year out to 50 years beyond the year of intake. The bioassay records used as input for DOSEXPRT are extracted from the Martin Marietta Energy Systems Occupational Health Information System (OHIS). DOSEXPRT implements a set of algorithms with parameters governing the translocation, retention, and excretion of the nuclide contained in data files specific to the nuclide. These files also contain dose-per-unit-intake coefficients used to compute the committed dose equivalent for the intakes in the year. Annual organ and effective doses are computed using additional dose-rate files that contain data on the dose rate at various times following a unit intake. If measurements are presented for more than one assay for a given nuclide, DOSEXPRT estimates the intake by applying weights assigned in the nuclide file for each assay. DOSEXPRT is accessed off the OHIS MENU No. 4 and designed to be run as a batch processor, but can also be run interactively for testing purposes
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Model for the age-dependent skeletal retention of plutonium
A mathematical model of the metabolic and physiologic processes involved in the retention and translocation of plutonium in the body. The implications of the model concerning the dose as a function of age to radiosensitive tissues of the skeleton are examined. 16 references, 1 figure. (ACR
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The reference individual of radiation protection
The 70-kg {open_quotes}standard man{close_quotes} representing a typical Western adult male has been used in physiological models since at least the 1920s. In 1949 at the Chalk River conference, health physicists from the U.S., UK, and Canada agreed on the concept of a standard man to facilitate comparison of internal dose estimates. The 70-kg standard man included specifications of the masses of 25 organs and tissues, total body content of 15 elements, total water intake and output, water content of the body, and some anatomical and physiological data for the respiratory and gastrointestinal tracts. In 1959, in its Publication 2{sup 2} on permissible doses for internal radiation the International Commission on Radiological Protection (ICRP) modified standard man. In 1963 the ICRP established a task group to revise and extend the standard man concept. The name was changed later to Reference Man and the task group`s work was published in 1975 as ICRP Publication 23{sup 3}. Publication 23 similar to Publication 2, updates and documents the sources of the data. Data on women, children, and fetuses were also collected, where available, but these data were limited primarily to anatomical data and only a few reference values were established for these groups. Information assembled during the course of the effort on the Reference Man report was used at Oak Ridge National Laboratory (ORNL) to construct a mathematical representation of the body (a phantom) that was suitable for use with Monte Carlo methods in the calculation of organ doses. That effort was undertaken to improve estimates of dose from photon-emitting radionuclides residing within organs, so-called internal emitters. The phantom, although updated throughout the years, remains today as the basis for organ dose estimates in nuclear medicine and radiation protection and underlies the radiation risk data derived from the epidemiologic studies of the atomic bomb survivors of Hiroshima and Nagasaki
Neutron and photon fluence-to-dose conversion factors for active marrow of the skeleton
Calculation of the absorbed dose to active marrow is a complex problem because charged particle equilibrium may not exist near a soft tissue-bone interface and it is difficult to model the intricate intermixture of soft tissue and bone in the skeleton. This study provides the first definitive calculations for a variety of bones and a wide range of neutron and photon energies. We avoid the assumption of a special geometry by using measured chord-length distributions to represent the microstructure of trabecular bone which contains the active marrow. Results of our calculations for neutrons and photons with energies up to 20 MeV are presented as dose response factors. The response factors can be applied in radiation transport calculations of absorbed dose in active marrow from photons and neutrons externally incident on the body and photons produced by neutrons interactions within the body. 34 references, 6 figures, 2 tables