The Retention of 226Ra in Human Soft Tissue and Bone; Implications for the ICRP 20 Alkaline Earth Model

Abstract

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.

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

“…A longer removal half-time from ST1 for strontium than calcium was needed to obtain a good fit to measurements of injected 85 Sr in human soft tissues at about 1-4 mo after injection. Fractional deposition of strontium in the "tenacious-retention" compartment, ST2, was set to yield reasonable agreement with the estimate of Schlenker et al (1982) that about 1% of the body's natural strontium resides in soft tissues in the average adult.…”

“…All four elements have similar skeletal uptake and distribution at early times after injection (Ellsasser et al, 1969;Wood et al, 1970;Liniecki, 1971;Stather, 1974;. Within a few months after administration of isotopes of calcium, strontium, barium, or radium, nearly all of the remaining total-body activity is associated with bone mineral (ICRP, 1973;Schlenker, 1982).…”

“…Kinetic analysis of data for human subjects administered radiocalcium indicate that readily exchangeable calcium in soft tissues represents an estimated 0.35% of total-body calcium in a middle-aged adult human (Heaney 1964, Borle 1981, Schlenker et al 1982. Plasma contains about 0.03% of totalbody calcium in the adult.…”

Radium in humans: A review of U.S. studies

“…Schlenker et al (1982), after an examination of data on the distribution of radium in soft tissue, found that the ICRP 20 function did not describe the actual distribution of radium between soft tissues and bone in the human body. They modified the values of certain parameters in the equation so that a much better fit was obtained.…”

AGE-DEPENDENT DOSE ASSESSMENT OF 226Ra FROM BOTTLED WATER INTAKE

“…226 Ra is radiotoxic and it follows the metabolic path of calcium. As a "bone seeker," it lodges principally in the skeleton (Schlenker et al 1982). 226 Ra and calcium have different rates of movement between plasma, bone, and soft tissues, and they have different rates of urinary and fecal excretion (ICRP 1993).…”