Carrier-free 166Ho from 166Dy/166Ho biomedical generator system

Abstract

Holmium-166 (166 Ho) is a potential candidate for various therapeutic applications (1-2) due to its attractive properties which include emission of high-energy β− particles (Eav=666 MeV), an appropriate half-life (t1/2=26.4 h) and decay to stable daughter. ln addition, 166Ho has chemical characteristics suitable for protein labelling through bifunctional chelates. Holmium-166 also emits a low intensity and low energy γ-rays (80 keV, 6%) suitable for imaging. Due to the absence of high energy γ-rays in its decay, 166Ho may be used for outpatient therapy without significant external radiation to other individuals.

Although 166Ho, with a moderate specific activity, can be produced by a simple neutron capture reaction, interestingly, its radionuclidic parent (81 .5-h 166Dy) can serve as a source of high specific activity 166Ho. ln certain applications, such as protein labelling, the use of a high specific activity radioisotope is essential. In addition, generator produced 166Ho is free from 1200-γ 166mHo. This isotope is unavoidably coproduced with 166Ho by the 165Ho[n,γ] reaction (3).