90Sr +90Y Bremsstrahlung Efficiency in Bone

Abstract

The bremsstrahlung efficiency (x-ray photon output/[mu]c) of beagle bones labelled with Sr90 + Y90 has been determined relative to the efficiency in water. The bremsstrahlung counting rate between 50 and 1000 kev from the individual bones was compared to that from a water-filled standard using an 8 x 4 in. NaI(Tl) crystal. Efficiencies were found to vary linearly with both the density and the computed effective atomic number (Zeff) of the fresh, intact bone. The empirical expressions developed from the data, relating relative bremsstrahlung efficiency to Zeff and density were, efficiency = 0.37 + 0.63 (density) and, efficiency = 0.215 + 0.119 (Zeff). For intact beagle bones averaging 1.48 g/cm3 (Zeff = 9.1), efficiencies were about 1.3 times that of a water-filled phantom. No great effects on efficiency were observed which could be ascribed to uniform versus nonuniform Sr90 labelling or to bone size.