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Journal Article

Retention and Skeletal Dosimetry of Injected 226 Ra, 228 Ra, and 90 Sr in Beagles

Ray D. Lloyd, Charles W. Mays, David R. Atherton, Glenn N. Taylor and Marvin A. Van Dilla
Radiation Research
Vol. 66, No. 2 (May, 1976), pp. 274-287
DOI: 10.2307/3574396
Stable URL: http://www.jstor.org/stable/3574396
Page Count: 14
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Retention and Skeletal Dosimetry of Injected 226 Ra, 228 Ra, and 90 Sr in Beagles
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Abstract

Total-body retention has been determined by in vivo counting in beagles injected with 226 Ra (125 dogs), or 228 Ra (78 dogs), or 90 Sr (96 dogs). The radionuclides were administered intravenously in a citrate buffer solution when the animals were about 1.4 years of age. Retention measurements now extend to more than 14 years after injection; therefore, future revision of these retention equations appears unlikely since the median life-span in our control beagles is about 12.7 years. Dogs injected with about $10\ \mu {\rm Ci}\ {}^{226}{\rm Ra}/{\rm kg}$ had a higher long-term retention than those receiving 0.04 to about $4\ \mu {\rm Ci}\ {}^{226}{\rm Ra}/{\rm kg}$. This has been interpreted as a consequence of radiation damage to the bone remodeling processes at high 226 Ra concentrations. Total-body biological retention [R(%)] at t days could be described by the following functions. 226 Ra, for 1400 days after the injection of 10 μCi/kg: $R(\%)=41e^{-0.56t}+10e^{-0.073t}+20e^{-0.0049t}+29e^{-0.00030t}$, 226 Ra, for 5200 days after the injection of 0.04 to 4 μCi/kg: $R(\%)=25e^{-0.98t}+21e^{-0.27t}+21e^{-0.016t}+18e^{-0.0020t}+15e^{-0.00015t}$, 90 Sr for 5000 days after injection: $R(\%)=36e^{-0.95t}+29e^{-0.12t}+10e^{-0.0091t}+12e^{-0.0019t}+13e^{-0.00015t}$. The 228 Ra retention data were not analyzed numerically, but visual inspection of the curves prepared for individual dogs indicated that 228 Ra retention could be described adequately by the retention equation derived for dogs given 0.04 to $4\ \mu {\rm Ci}\ {}^{226}{\rm Ra}/{\rm kg}$. The average skeletal radiation dose rate and cumulative radiation dose were calculated for each beagle injected with 226 Ra or 228 Ra or 90 Sr using the appropriate retention equation, normalized to each dog's individual retention measurements. Allowance was made in the 226 Ra calculations for the changing skeletal retention of 222 Rn and its radioactive daughters; in the 228 Ra calculations for the diminution of 228 Ra activity by radioactive decay as well as for the ingrowth and skeletal retention of 228 Th and its radioactive daughters; and in the 90 Sr calculations for the diminution of 90 Sr concentration by radioactive decay and the escape of β-energy from bone. The half-time (4621 days) of the longest-lived component in the 90 Sr retention equation was similar to that for the lower-level Ra dogs. This may reflect the net remodeling rate of cortical bone in the beagle skeleton.

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