EXCITATION-FUNCTIONS OF PROTON-INDUCED REACTIONS ON COBALT - PRODUCTION OF NO-CARRIER ADDED NI-57, A POSITRON EMITTING LABEL FOR DOXORUBICIN

Excitation functions were measured, by the stacked-foil technique, for the Co-59(p, 3n)Ni-57 and Co-59(p, 4n)Ni-56 nuclear reactions from threshold up to 60 MeV. The excitation function for the Co-59(p, 3n)Ni-57 reaction shows a maximum cross section of 13.8 +/- 1.5 mb at 38 MeV. The optimum energy range for production of Ni-57 was found to be 41 --> 26 MeV resulting in an experimental thick target yield of 19.3 MBq/muAh) (522 muCi/muAh). The level of the Ni-56 impurity is only 0.21% at EOB giving a Ni-57 product of 99.7% radionuclide purity at the time of use (24 h post EOB). Cross section data for the production of Ni-56, Co-56, Co-57, Co-58, Mn-52, Mn-54 and Cr-51 are also presented. A radiochemical procedure, based on cation-exchange chromatography, for the separation of radionickel from an activated cobalt target and other radiochemical and chemical impurities, has been developed. The Ni-57 activity was eluted, using 2 M HCl from a Dowex-50W x 8(H+) column, in a 95% radiochemical yield (15 mL). The Ni-57 has been used to label the anti-cancer drug, doxorubicin, thereby providing the means for pharmacokinetic and pharmacodynamic studies of this compound using positron emission tomography. The labelling has been optimized to give a radiochemical yield of >94%.