Synthesis and Evaluation of 157Gd-Labelled DNA Ligands

Abstract

The interest in the potential role of 157Gd in neutron capture therapy1,2,3 obviously stems from its very high thermal neutron capture cross section. It is about 60 times higher than that of 10B However, unlike the fission reaction associated with boron neutron capture, 157Gd undergoes an n-gamma reaction. The very high energy of the gamma photons is in marked contrast to the limited range of the fission products of boron neutron capture. That limited range, of the order of a cell diameter, is a crucial feature of the rationale of boron neutron capture therapy. However, some of the gamma energy from the 157Gd capture reaction is converted, with the emission of conversion electrons4. More importantly, the vacancies left by conversion electrons result in the emission of Auger electrons. The Auger electron emission, exemplified by the Auger emitting isotope 125I, is a focus of intense radiochemical damage, and the range of damage is limited to molecular dimensions5–8.