9OSr +90Y bremsstrahlung efficiency predicted for humans

Abstract

Bremsstrahlung x-rays are produced when energeticβ-particles are emitted and absorbed. Measurements of total-body bremsstrahlung efficiency (x-ray photon output per εCi⁹⁰Sr in the body, relative to that in water) have been made in the intact mouse, rat, rabbit, and dog sacrificed 2 weeks after the injection of⁹⁰Sr +⁸⁵Sr. Efficiencies were determined by a comparison of the bremsstrahlung output from⁹⁰Sr + its daughter⁹⁰Y and the gamma-ray emission of⁸⁵Sr. Results were checked by aβ-assay of the ashed animals. Bremsstrahlung efficiencies averaged 1.10 in a 0.04 kg mouse, 1.14 in a 0.13 kg rat, 1.23 in a 2.6 kg rabbit, and 1.32 in an 8.5 kg beagle. Extrapolating to a 70 kg human, a relative bremsstrahlung efficiency of about 1.4 is predicted. An estimate was made of the⁹⁰Sr body content in a former dial painter based on in vivo counting and a bremsstrahlung efficiency of 1.39 predicted for a 55 kg human female by these animal data. Our value of 1.42 ± 0.08 μCi⁹⁰Sr was in good agreement with corresponding results reported for this subject by 8 other laboratories.