We have adjusted the ICRP model of alkaline earth metabolism to fit data on the *"Ra content of 87 samples of soft tissue from 17 persons who received radium by injection or ingestion 5 days to 53 yr before measurement. The fitted functions indicate that soft tissue retention rises to 58% of the whole body retention at 18 days after single intake, and then falls steadily reaching 33% at 100 days and 6% at 1000 days. The adjusted model was also found to fit data on bone retention in 5 persons 8-467 days after injection. For both types of tissue, the new functions differ substantially from those originally published. The adjustments improve or do not significantly reduce the model's ability to fit other radium data.The fits to soft tissue and bone data were achieved by changing the quantity 8 in the ICRP model from its original value for radium I0.06236 ( l-RBODy)}-2.410 to {0.1247( 1 -RBODy)}-2'410, where R B o D y is the whole body retention function. This forced new values for five model parameters for radium: / 3 = 0.6254, w = 1.436, fc = 5.629, v = 1.521, r = 0.9953. Also changed are the empirical values for the percentages of the body's natural alkaline earth contents which lie in soft tissue: Ca(0.28%), Sr(0.98%), Ba(4.7%), ZZ6Ra(S.5%).For use in dosimetry, effective retention integrals are given for 224226.228 Ra and for '=Th in soft tissue, on bone surfaces, in bone volume, and in the whole body. Integration times of 1 yr, 50yr and infinity are used. For 226.228Ra, the soft tissue integrals are reduced by factors of 1.5-2.5 below the values originally published; for Z24Ra, the reduction factor is about 1.1. The bone volume integrals increase for all isotopes; the percentage increase, about loo%, is greatest for 224Ra.A reanalysis of the autoradiographic data on 226Ra in bone has been carried out using the adjusted functions. The best fit results with dc = 1.5 rather than with the previous value, 10, indicating that the so-called modified version of the ICRP model may be unnecessary. An examination was made of the ability of the ICRP model to predict the outcomes of experiments to which the model functions had not been previously fitted. Results were positive.
The natural RaD (PbZ1O) concentration in man has been determined from measurement of the RaF (PozlO) in bone samples obtained from surgery and autopsy of unexposed individuals, mostly from Illinois. About 63 per cent of the RaD is in the skeleton in apparent equilibrium with RaF and, within a factor of 2, it is uniformly distributed in the skeleton. The average RaD concentration found in 128 bone samples was 0.146 f 0.020 pc/g ash as compared to an average Ra226 concentration of 0.037 0.007 pc/g ash. Little correlation between the two nuclides was observed. The average RaD concentrations in the skeleton were 0.161 pc/g ash in men and 0.119 pc/g ash in women. These concentrations were generally higher in trabecular than in cortical bone, 0.184 and 0.105 pc/g ash, respectively. No particular correlation was found between the residence histories of the donors and the RaD concentrations in their skeletons. Calculations based on some of the metabolic parameters of lead and on the known concentrations of RaZz6, RnZz2 and RaD in the human biosphere, show food and air to be the major contributors of RaD in the subjects studied. The RaDEF decay chain is shown to contribute a radiation dose to the human skeleton more than double that from Ra226 and about equal to that from RaZz6 and RaZz8 combined.
We made radiochemical determinations of 226Ra and the 228Ra-decay product, 228Th, in samples of bone from former Ra dial workers who belonged to a major cohort of Ra-exposed persons under study for health effects at our institution. Most of the former workers were long-term residents of two communities supplied with drinking water containing elevated natural levels of 228Ra and 226Ra, so determinations also were made of radioactivity in samples of bone from long-term residents not occupationally exposed to Ra. The 228Th activity of the bones of the former workers, after correction for the presence of natural radioactivity, showed that some had significant occupational intakes of 228Ra, contrary to published reports that 228Ra was never used by the Illinois company that had employed the cohort of early workers. For 14 workers hired in the years 1920-23, the calculated ratio of the occupational intake of 228Ra to 226Ra activity averaged 0.15 (coefficient of variation 0.65), whereas for three workers hired in 1924, it was not significantly different from zero (mean 0.05, coefficient of variation 1.5). The risk of radiogenic cancer for the typical worker hired before 1924 may have been nearly twice that incurred in the absence of the 228Ra component of the Ra intakes.
Analyses are presented of the ratios of 226Ra to calcium in over 650 samples of compact and cancellous bone from 66 female and 26 male subjects who had died from less than 1 to 60 yr after first exposure to radium. The 226Ra/Ca ratios were normalized to the terminal 226Ra skeletal content. The 226Ra/Ca ratios for vertebrae were essentially identical to those for other cancellous bone for a given subject. Comparisons of the data with predictions of the ICRP model of alkaline earth metabolism show that for female cancellous bone the normalized 226Ra/Ca ratios tended to be greater than predicted, while those for female cortical bone (femoral and tibial shaft) tended to be less. The data for males were fitted better by the model. A modification of the model to reduce the amount of radium deposited in soft tissue fitted the data better in some respects. A straight line linear least squares fit to the data appeared to fit as well as, or better than, the models. A radiation effect was suggested in that the normalized 226Ra/Ca ratio for vertebrae relative to the ratio expected increased with skeletal absorbed dose for vertebrae. However, no such effect was apparent for compact bone or for the cancellous bone as a whole.
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