Correcting Neutron Dosimetry Records for Epidemiology. Part II: Dose Imputation and Uncertainty
D.J. Strom; R.I. Scherpelz; J.J. Fix; and R.J. Traub (Pacific Northwest National Laboratory)
The use of occupational radiation monitoring records as a basis for developing a quantitative exposure variable for epidemiologic research presents an ongoing challenge. The challenge is much greater for neutron radiation than for photons or electrons, since neutron measurement technologies have evolved from wholly inadequate in the 1940s, through marginal for fast neutrons during the 1950s and 1960s using NTA film, through barely tolerable with the advent of thermoluminescent neutron dosimeter (TLND) technology in the early 1970s, to modern multi-element TLND technology available today. In a previous paper, we defined dosimeter technology combinations as a dosimeter type used in conjunction with a calibration neutron energy spectrum, a workplace neutron energy spectrum, and a recorded quantity. In that paper, bias factors were presented for each dosimetry technology combination. In this paper, we present methods to impute doses for workers for whom measurements were not made or were inadequate. Imputation is based on work histories and neutron-to-gamma ratios. Those ratios result in large uncertainties because they typically were measured the first year that TLND was introduced. Asymmetric, lognormally-distributed uncertainty factors are developed to account for uncertainties in dosimeter response, neutron energy spectrum, and irradiation geometry; how well the ICRP-74 phantom represents each individual; and data censoring, imputation, and lost or damaged dosimeters. Ordinal confidence categories are also developed to flag imputed doses and inconsistent or otherwise suspicious results. *Pacific Northwest National Laboratory is operated for the U.S. Department of Energy by Battelle under Contract DE-AC06-76RLO 1830.