Showing papers by "Richard W. Leggett published in 1984"

Estimating dose rates to organs as a function of age following internal exposure to radionuclides

Abstract: The AGEDOS methodology allows estimates of dose rates, as a function of age, to radiosensitive organs and tissues in the human body at arbitrary times during or after internal exposure to radioactive material. Presently there are few, if any, radionuclides for which sufficient metabolic information is available to allow full use of all features of the methodology. The intention has been to construct the methodology so that optimal information can be gained from a mixture of the limited amount of age-dependent, nuclide-specific data and the generally plentiful age-dependent physiological data now available. Moreover, an effort has been made to design the methodology so that constantly accumulating metabolic information can be incorporated with minimal alterations in the AGEDOS computer code. Some preliminary analyses performed by the authors, using the AGEDOS code in conjunction with age-dependent risk factors developed from the A-bomb survivor data and other studies, has indicated that the doses and subsequent risks of eventually experiencing radiogenic cancers may vary substantially with age for some exposure scenarios and may be relatively invariant with age for other scenarios. We believe that the AGEDOS methodology provides a convenient and efficient means for performing the internal dosimetry.

A measure of model reliability.

Abstract: A method for evaluating predictive models is developed by giving a precise and statistically meaningful interpretation to the statement that a model is accurate within a factor of k. This method is applicable to any model for which there is a set [y1,..., yn] of observations corresponding to a set [x1,..., xn] of model predictions. We define a geometrically intuitive measure of model reliability kg in terms of the ratios yi/xi and a statistically rigorous measure ks in terms of 1n (yi/xi). For reasonably accurate models, kg and ks are in virtual agreement and thus can be used interchangeably as a reliability index. The index ks estimates a model parameter of the form exp[(V1 + V2)1/2], where V1 describes an observational variance and V2 is related to an uncertainty associated with the model itself. The computed value for ks is not unique but depends on the sample of observations. The probability distribution of ks can be characterized provided the observational distributions are lognormal, independent, and satisfy a homoscedasticity condition. These requirements are often satisfied by quantities of interest in radiation risk analyses. The reliability indices kg and ks may be applied even if the underlying observational distributions are not lognormal, although the probability distribution of ks cannot be characterized in this case.

An assessment of health risk from radiation exposures.

Abstract: A methodology has been developed to assess potential hazards from low-level exposures to radioactive pollutants. Estimates of dose rates to reference organs from internal and external exposure pathways (inhalation of contaminated air, ingestion of contaminated food or water, immersion in contaminated air, and exposure to contaminated ground surfaces) are computed with contemporary dosimetric models. These dose rates are used in a life-table analysis to estimate the radiation-induced cancer deaths and resultant years of life lost in an exposed cohort of 100,000 persons, all simultaneously liveborn and subject to the same risks of dying from competing causes (including natural background radiation). Estimates of the potential health risk are tabulated for approx. 150 radionuclides for each of the exposure pathways; results are summarized in terms of the probability of premature radiation-induced death for a member of the cohort due to incremental radiation exposure, and the average number of years of life lost per incremental fatality. The estimates of radiation-induced mortality generated by these methods provide a useful means of quantifying radiation risk; however, these estimates may be subject to large uncertainties, and can be best interpreted as a measure of the relative degree of hazard associated with exposures to various radionuclides through several exposure pathways.