The influence of growth and${\rm Na}_{3}{\rm Ca}\text{-}{\rm DTPA}$ treatment on the microscopic distribution of Am(III) in the distal femora of 8-week-old female rats were examined by means of solid-state nuclear-track detectors and an electronic scanning technique. The iv dose of$[{}^{241}{\rm Am}]\text{citrate}$ was 30 μCi/kg; Ca-DTPA was administered ip once weekly in a dose of 30 μmole/kg, and the first dose was injected 1.5 hr after the241 Am. The animals were sacrificed 7, 14, 28, and 56 days after the241 Am injection. The distribution of241 Am was presented as computer-generated scan plots giving quantitative information about radiation dose rates. The redeposition of241 Am in newly formed bone tissue between the zone of heavy initial uptake and the epiphyseal cartilage plate was absent in the case of DTPA treatment. There was a diminution of activity by DTPA in the metaphyseal band to 40% of the control values on the 7th day and to 26% on the 56th day. While DTPA does not significantly affect removal of the epiphyseal deposit of241 Am, there is a continuing effectiveness in the metaphysis and diaphysis, yielding a reduction to 70% of the control radioactivity at the 7th day, and 28% at the 56th day. Bone remodeling tended to increase the nonuniformity of the dose-rate distribution, which, for example, led to an enhancement of the maximum dose rates in the metaphyseal band. This increase of the nonuniformity of the dose-rate distribution is even enhanced by DTPA treatment. The information contained in the dose-rate scans was reduced to probability density curves and compared for the effects of ageing and DTPA.

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