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Evaluation and Control of Internal Radiation Exposures on the Basis of Committed Dose Equivalent
Published in Kenneth L. Miller, Handbook of Management of Radiation Protection Programs, 2020
To account for the total dose equivalent and committed risk* associated with the intake of a radionuclide, a committed dose equivalent is used. The committed dose equivalent to a given target organ or tissue is the expected dose equivalent averaged throughout that organ or tissue in the 50-year period following the intake of the radionuclide. For historical perspective and to show the connection of the previous to the current recommendations of the International Commission on Radiological Protection (ICRP) and the National Council on Radiation Protection and Measurements (NCRP), the relationships between the primary committed dose equivalent limits and derived limits are summarized as follows.
Exposure Assessment
Published in Samuel C. Morris, Cancer Risk Assessment, 2020
Exposure can be expressed in several different ways. An individual can be exposed to a certain amount of arsenic in water over a given period. This might be a day or a lifetime. If the concentration in the water is 0.1 mg/1, that might be taken as the exposure, or, if the individual consumes 2 liters of water per day, the individual exposure might be expressed as 0.2 mg/day. If 1000 people in a community have the same exposure, the population exposure might be expressed as the product, 200 person-mg/day. In the case of internally taken radioactive materials such as irradiates the body over a long period of time. This is called a committed dose, since, by ingesting the cesium, the person is committed to a continuing dose until all the cesium has decayed or been biologically removed. Like exposure, committed dose may also be expressed as either an individual or a population commitment. It may also be expressed as an environmental commitment. The Chernobyl accident, for example, released 137Cs into the biosphere. With its 30-year half-life, it will remain available in the foodchain to be ingested by people for decades. This is an environmental commitment. A toxic chemical leaching from a hazardous waste dump into an aquifer presents a similar environmental commitment, sitting there waiting for someone to drink it.
Dosimetric Models
Published in Shaheen A. Dewji, Nolan E. Hertel, Advanced Radiation Protection Dosimetry, 2019
In ICRP Publication 30, an entirely new system of internal dose assessment was established. For the most part, this system has been adopted into law and has been in use in the United States since 1990. The committed dose equivalent was defined as the total dose equivalent to an organ or tissue over the 50 years after intake of a radioactive material. The dose equivalent (or the committed dose equivalent) is proportional to the product of the total number of nuclear transformations occurring in the source tissue over the time period of interest and the energy absorbed per gram of target tissue per nuclear transformation of the radionuclide, modified by the appropriate quality factor. In the symbolism used by the ICRP, this becomes:
Potential improvements in brain dose estimates for internal emitters
Published in International Journal of Radiation Biology, 2022
Richard W. Leggett, Sergei Y. Tolmachev, John D. Boice
The preponderance of published data on accumulation of elements in the brain come from studies on laboratory animals. Best available data for the human brain generally come from autopsy studies of occupationally or environmentally exposed subjects. Such autopsy data were found for seven of the elements addressed here: Cs, Mn, Pb, Ra, U, Pu, Am. The brain models applied here to these elements were required to be consistent with the element-specific brain contents (as a percentage of the systemic content) determined in the autopsy studies. The brain model for Cs is a well-supported model based on data on the blood perfusion rate in the human brain and measurements of the fraction of blood-borne Cs extracted by the brain during passage of blood through the brain, in addition to autopsy measurements of environmental 137Cs in human tissues including brain. For Mn, Pb, Ra, U, Pu, and Am, data for laboratory animals were used to model the rate of accumulation in the brain starting at the beginning of exposure. For radioisotopes of these six elements addressed here (54Mn, 210Pb, 226Ra, 234U, 239Pu, and 241Am), analyses were performed to determine the sensitivity of the dose coefficients for brain, based on explicitly depicted brain models, to uncertainties in the interspecies extrapolation of the data. It was found that the dose estimates for brain were largely determined by the requirement that predictions of the brain model be consistent with the results of the autopsy data. Stated differently, the dose coefficients for brain for 54Mn, 210Pb, 226Ra, 234U, 239Pu, and 241Am based on explicit brain models were found to be only moderately sensitive to uncertainties (within reasonable uncertainty bounds) in the use of animal data to predict brain kinetics of the element at early times after intake. For example, if the rate of uptake of 239Pu by the brain was varied within a factor of 2 of the value indicated by data for dogs and the biological half-time in the brain was covaried so that model predictions remained consistent with USTUR autopsy data, the derived committed dose to the human brain varied within 20% of the value based on the explicit brain model applied here to 239Pu.