Oxidation of terbium (III) as a first step towards high purity terbium-161 for medical applications
Radiopharmaceuticals are medicinal formulations containing radioisotopes, which are used for diagnosis or therapy; and the ones based on radioactive terbium (Tb) isotopes can be used for radiotherapy, where a specific tumor is targeted and selectively irradiated. One of these isotopes is terbium-161 (161Tb), a beta emitter, and can be produced in the Belgian Reactor 2 (BR2) at SCK•CEN by irradiation of gadolinium-160 (160Gd) targets: when a neutron is captured by 160Gd this yields 161Gd, which decays to 161Tb. However part of the produced 161Tb will have decayed to the stable isotope 161Dy. Therefore, to isolate and purify 161Tb from the dissolved irradiated 160Gd targets, a method must be developed to separate Tb from the other lanthanide elements and impurities. Due to the similarity in chemical properties, the separation of adjacent lanthanides is highly challenging. The most efficient separation method is using a cation exchange resin with α-hydroxyisobutyric acid (α-HIBA) as eluent has been used to isolate 161Tb from milligram amounts of 160Gd. There are however several downsides to this separation process such as long duration of the separation, not obtaining a complete separation when small amounts of Tb-161 is isolated from a lanthanide matrix, and the decrease in pure 161Tb fraction due to severe peak broadening and increased tailing with increasing target size. Because of these important disadvantages, especially when larger targets have to be processed, a new and improved separation method needs to be developed to produce considerable amounts of 161Tb for radiopharmaceutical use. The proposed strategy in this doctoral research is to dissolve the irradiated targets and selectively oxidize Tb(III) into Tb(IV) prior to the separation process. The high chemical stability of Tb(III) requires strong oxidizing agents to form Tb(IV). Therefore the objective is to develop an electrochemical method to oxidize Tb(III) to Tb(IV); since the applied current is used for oxidation, no additional chemical need to be used and a higher level of control can be achieved over the process.