A Biokinetic Model for 137Cs

Abstract

An improved biokinetic model for 137Cs in humans was developed based on an analysis of data obtained from individuals internally contaminated during an accident in Goiania, Brazil, and other data. Seventeen children (ten girls and seven boys 1-10 y old), ten adolescents (four females and six males), and thirty adults, (fifteen females and fifteen males contaminated in the accident in Goiânia contributed to this study. 137Cs retention was determined through periodic measurements in a whole-body counter. In addition to the data on 137Cs retention from these individuals, data from a study on the metabolism of 137Cs in immature, adult, and aged Beagle dogs and data from the literature were used in the formulation of the 137Cs biokinetic model presented. Mathematically, the retention of cesium is described by three exponential terms, and the retention model is based on a step function of body weight. When the ICRP Publication 56 model for cesium was compared to the model suggested in this paper, it was determined that the ICRP model predicts lower effective doses in 5-y-old children and higher effective doses in infants, adolescents, and adults.

Cesium-137 Decorporation Model

“…Since the model incorporated in this work is based on adult male physiological parameters, our retention values are compared to human data , Melo 1997 for adult males and the ICRP model (1989) for adult males.…”

“…This comparison of data is shown in Figure 11. The data is represented by four subjects of a controlled study by Richmond (1962), five controls in a study by Lloyd (1972, and five non-chelated men in Goiânia accident (Melo 1997(Melo , 1998. While significant individual variability exists, the model adequately represents the general whole-body retention of cesium in adult males.…”

“…Based on the human and animal experimental data, a whole-body retention function for cesium was determined to have a short-term and long-term component in a number of studies (Boecker 1969, Leggett 1986, Melo 1997. As described in section 4.5.2, Cs retention has been described by the following function:…”

Reliability of Current Biokinetic and Dosimetric Models for Radionuclides: A Pilot Study

“…Although there is some overlap in individual halftimes for male and female subjects, the mean half-time for the female subjects is 15-35% lower than that for male subjects in each of these studies. The long-term half-time of cesium in the body usually is reduced during pregnancy to about two-thirds of the value when not pregnant, perhaps due to increased aldosterone levels in blood during pregnancy Zundel et al, 1969;Leggett, 1986;ICRP, 1989;Melo et al, 1997;Thornberg and Mattsson, 2000). Schwartz and Dunning (1982) collected data from the literature on the equivalent biological half-time of 137 Cs in the human body.…”

“…Data from three studies (Lloyd et al, 1973;Lebedev and Yakovlev, 1993;Melo et al, 1997) are shown in Figure 5.6. Typical longterm half-times as a function of age and gender are given in Table 5.1 (McCraw, 1965;Lloyd et al, 1973;Leggett, 1986;Lebedev and Yakovlev, 1993;Melo et al, 1997;Leggett et al, 1998). …”