Abstract
1153
Objectives Routine clinical application of 68Ga pharmaceuticals is close to becoming reality thanks to several post processing methods, such as fractionation or ion exchange, that provide 68Ga at a purity meeting the requirements of pharmaceutical legislation. Ion exchange procedures can be performed with cation- (CEX) or anion- (AEX) exchange resins. The use of acidified solutions of acetone, ethanol or NaCl in combination with CEX resins show excellent results in labelling of various substances. In this work we compared these CEX-solvent system combinations for labelling three different model substances (DATAm, DOTATOC and NO2APBP).
Methods A 68Ge/68Ga Obninsk generator providing 400 MBq 68Ga (85 kBq 68Ge breakthrough) was used. Preconcentration and purification of the initial generator eluate was carried out using three CEX based post-processing methods. Clinically approved buffer solutions or water were used for labelling media. Each substance was labelled conventionally at two temperatures or two pH values, and the results compared in terms of yield and reproducibility.
Results Overall, the ethanol system resulted in the quickest labelling (5 min / ≥ 90%; 20 min/ > 95%), and was accompanied by a high reproducibility (σ < 7.5). Although the acetone system showed excellent yields (86-99% after 10 min) as well, a following workup procedure is necessary to remove all acetone present before injection. For the NaCl system yields after 20 min were < 95%, and an overall lower reproducibility (σ < 18) was found.
Conclusions All three methods were used successfully for labelling of the model substances. Considering future clinical application of 68Ga, the ethanol system appears to be a very promising tool for purification of intial generator eluate and subsequent labelling. The advantages of ethanol over acetone also extend to its action as a radiolysis inhibitor and yield optimizing agent, with its approval for being used in humans seen as the significant benefit.