The potential of ytterbium 169 in brachytherapy: a brief physical and radiobiological assessment.

Ytterbium 169 (half-life 32 days; mean gamma emission 93 keV, after excluding photons of energy less than 10 keV) is a radionuclide with interesting potential for brachytherapy applications. Although not yet commercially available, its possible application as a clinical radionuclide is currently being considered by Amersham International. This article presents an assessment of some properties of the nuclide that may be clinically relevant. Use is made of some new ideas that allow quantification of the likely dose homogeneity that can be obtained in a brachytherapy distribution, and in this context ytterbium 169 is shown to be superior to some currently available brachytherapy nuclides. The assessment also uses recent extensions to the linear-quadratic model to consider the likely radiobiological implications associated with the use of the nuclide. From this it is suggested that the main potential for ytterbium 169 would be as a source that may be re-used for a number of short-term applications, rather than as a permanently implantable nuclide.