Radiation Dose Reconstruction for Epidemiologic Uses (1995) / Chapter Skim
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5 Radiation Dose Assessment
5 Radiation Dose Assessment
Pages 40-50
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From page 40... ...
SOURCES OF EXPOSURE Three sources of radiation exposure that must be taken into account in estimating the dose either to representative or to specific persons are: (a) external exposure due to submersion in contaminated air or due to radiation from an overhead plume or from radionuclides deposited on the ground, (b)
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From page 41... ...
Calculation of the dose to the whole body or to a specific organ requires further information: the estimated duration of daily exposure (in hours) , the breathing characteristics of that individual, a model of the respiratory tract that allows calculation of the amount of airborne particles deposited in the airways, the physical and metabolic characteristics of the deposited radionuclide, and the size of the individual.
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From page 42... ...
As a result of this accumulation, measurements of radionuclides in tissue samples may provide a method of dose assessment when long-lived radionuclides are involved. The absorbed dose due to inhaled radionuclides can be calculated by means of an appropriate model that takes into account lung deposition, transpiration, organ distributions, and clearance rates (Loevinger and others 1991~.
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From page 43... ...
POTENTIAL CONSEQUENCES OF RADIATION EXPOSURE The biologic effects of ionizing radiation are better understood than are those of exposure to any other potentially harmful element or compound. In large doses, ionizing radiation clearly causes cancer in humans, but fortunately radiation is a relatively weak carcinogen.
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From page 44... ...
In other words, it might be reasonable to establish an effective dose commitment over so many years below which it makes little sense to waste huge sums of money for further quantification. To estimate health risks reliably, the most accurate estimate of dose to members of the public should be obtained.
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From page 45... ...
PRELIMINARY DOSE ASSESSMENT The purpose of a preliminary dose assessment is to determine the need for a study of the health effects resulting from the exposure of a population to radiation. A preliminary assessment will normally precede a comprehensive health effects study, but when there is evidence of epidemiologic effects or widespread public concern, the health study can be initiated in lieu of, or in parallel with, the preliminary dose assessment.
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From page 46... ...
In general, it is more useful to calculate annual dose rates and risks to reference individuals than to calculate risks based on committed effective doses. In addition, the overall dose to and risk of each cohort can be calculated by combining the representative results with the size and age structure of each cohort.
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From page 47... ...
The preferred dose estimate from a comprehensive assessment is the annual absorbed dose to the target organs of the body. For radiation exposures from external sources in the environment, the absorbed dose to body organs increases with decreasing body size; this effect is most pronounced at low photon energies and for absorbed dose to organs located near the middle of the body that are shielded by overlying tissue.
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From page 48... ...
The preferred dose estimate from an individual risk assessment is the annual absorbed organ dose. As with the comprehensive dose assessment, the radiation dose from internal sources as a result of either inhalation or ingestion can use PBPK models.
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From page 49... ...
Direct measurement of radionuclide content in the body and in environmental samples, and individual dose measurements (physical or biodosimetric) should be used for validation of model predictions wherever available.
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From page 50... ...
The most useful dose quantity In a preliminary dose assessment is the effective dose; in a comprehensive dose assessment or In the computation of an individual dose, the preferred dose estimate will be the annual absorbed organ doses from lowLET and high-LET radiations. However, it should be noted that published intake dose conversion factors are for committed doses.
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