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.
From the results of serial measurements of body 226Ra activity in 13 former luminous dial workers 30-60 y after relatively brief periods of intake of luminous compounds in adolescence or young adulthood, we determined the postmenopausal rate of elimination of Ra in percent of contemporary body Ra content per year. This rate was negatively correlated with the "reduced x-ray score," a measure of radiation osteonecrosis observed radiographically in the 13 subjects (r = -0.85, P less than 0.001). The clearance rates of subjects retaining low Ra activity were greater than predicted by retention models. We conclude that for those members of the Ra-exposed population under study for health effects at our institution who sustained the lesser degrees of macroscopic skeletal damage, present estimates of skeletal absorbed dose are systematically low, by at most a factor of 2.
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.
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