Long-term biological effects of the chronic, relatively uniform whole-body radiation exposure from internally deposited137 Cs are being studied in the beagle. This report summarizes metabolism and dosimetry data obtained during the first year after intravenous injection, the period during which most of the radiation insult was delivered. Sixty-six dogs were entered into the study, six with a mean initial137 Cs body concentration of 3800 μCi/kg and five groups of 12 dogs each with 2800, 1900, 1400, 970, and 0 μCi/kg. Two-component exponential functions described the whole-body retention during the first 60 days while the dogs were housed in individual metabolism cages. Approximately 85% of the initial body burden was associated with the long-term retention component with a mean effective and biological half-life of 32 days. Retention changes seen after transferring the dogs to the combination indoor and outdoor kennel runs are described in relation to food consumption, exercise, age, temperature, and external contamination. These data were used to calculate cumulative absorbed whole-body beta and gamma doses for each dog. No dose-related effects were observed in whole-body retention or the calculated doses. When the cumulative total body doses were expressed as rads per initial mCi <tex-math>${}^{137}{\rm Cs}/{\rm kg}$</tex-math> body wt, the total dose to 180 days was 680, of which 50% was delivered in the first 30 days and 90% in the first 90 days. The normalized dose rate decreased from an initial mean value of 18.5 rads/day/initial mCi <tex-math>${}^{137}{\rm Cs}/{\rm kg}$</tex-math> body wt to 8.2 at 30 days and 0.2 at 180 days. Tissue distribution data obtained from 11 dogs that died 19-81 days after injection yielded similar concentration data for individual tissues as have been reported for experiments involving lower activity levels of137 Cs. Calculated absorbed tissue doses based on these data were 0.6-1.5 times that calculated as an average whole-body dose.

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