Topographic Analysis of the Microdistribution of 241 Am in the Rat Femur as Influenced by DTPA Treatment

Abstract

The influence of growth and Na3Ca-DTPA [trisodium-mono calcium diethylenetriamine peutaacetic acid] treatment on the microscopic distribution of Am(III) in the distal femora of 8 wk old female rats were examined by means of solid-state nuclear-track detectors and an electronic scanning technique. The i.v. dose of [241Am]citrate was 30 .mu.Ci/kg; Ca-DTPA was administered i.p. once weekly in a dose of 30 .mu.mol/kg, and the 1st dose was injected 1.5 h after the 241Am. The animals were sacrificed 7, 14, 28 and 56 days after the 241Am injection. The distribution of 241Am was presented as computer-generated scan plots giving quantitative information about radiation dose rates. The redeposition of 241Am 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 the 7th day and to 26% on the 56th day. While DTPA does not significantly affect removal of the epiphyseal deposit of 241Am, 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 aging and DTPA.