Yttrium-90 (Y-90) is a pure beta emitter and belongs to group III. Its high Emax beta (2300 keV) has made it an attractive choice for therapy applications, in spite of the lack of gamma emission. Higher energy and hence longer particle range in tissues provide the ability to treat larger tumors. Yttrium-90 is generator-produced from its parent Sr-90 and is available with high specific activity (27). Its trivalent ion is commonly used for chelation purposes. Used as the citrate salt, it shows 80% uptake in the bones. In this form it has been used for pain palliation from metastatic disease. It has the chemical properties suitable for chela-tion to several commonly used compounds or macrocyclic ligands such as DOTA (31,32). Several chelated forms are being evaluated for therapy and simple effective labeling methods are available (33). In spite of the need to use a surrogate radioisotope for biodistribution studies, yttrium has gained acceptance in clinical practice because its high beta particle energy and the lack of gamma radiation make out-patient treatment feasible (34,35).

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