Preparation and animal biodistribution of 166 Ho labeled DOTA for possible use in intravascular radiation therapy (IVRT)

Owing to its favorable decay characteristics ( T 1/2 =27 h, E β(max) =1.85 MeV, E γ =81 keV) and its availability with a specific activity of 3.7–4.4 GBq/mg from a moderate flux reactor, 166 Ho can be considered as a potential radionuclide for intravascular radiation therapy (IVRT) using liquid‐filled balloons. In the present work, studies on the use of 166 Ho labeled 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) as a possible agent for IVRT for the prevention of restenosis has been initiated. 166 Ho was obtained by irradiating natural Ho 2 O 3 powder and DOTA was synthesized by a multistep procedure. The optimum protocol of radiolabeling of DOTA with 166 Ho was achieved by varying different reaction parameters. The complex was found to retain its stability for 7 days at room temperature. Bioevaluation studies carried out in Wistar rats showed that >95% of the injected activity was excreted within 3 h p.i. with almost no retention in any major organ. Both radiochemical and biological studies showed that 166 Ho labeled DOTA can be further explored as a potential agent for IVRT. Copyright © 2002 John Wiley & Sons, Ltd.