AN INNOVATIVE PET DETECTOR CONCEPT FOR TOF-INBEAM PET DOSIMETRY IN HADRONTHERAPY

Objectives: The reactor produced low-energy beta emitter Lu (T1⁄2 = 6.7 d) is used on a routine basis in the clinical targeted radiotherapy in nuclear oncology. Currently the radionuclide is commercially available in its c.a. and n.c.a form. Here an efficient use of Lu for radiolabeling can be limited by several factors such as quality of the radionuclide and the chemicals or suboptimal parameters of the radiolabeling reaction. Identification of critical factors as well as an interpretation of the results is, however, complicated and limited by the analytical techniques applied. Methods: C.a. and n.c.a. Lu preparations were obtained from different commercial suppliers. The radionuclide has been employed for the systematical preparation of Lu-DOTA-octreotate. Radiolabeling yields and achievable specific activity of the compound have been analyzed using conventional HPLC. For the characterization and better understanding of critical parameters of the process, species identification in the final product (e.g. radiolabeled compound) has been performed by means of LC-ESI-TOF. Isotope and specific activity analysis of the Lu of different origin have been additionally done by means of SF-ICP-MS. Results: We were able to obtain straightforward information about the radiolabeled compound and isotope such as structure, quality and even origin and isotopic composition of the radionuclide used for the reaction. LC-ESI-TOF allows an efficient identification of the different species in the final product such as unlabeled or contaminated precursors, giving worthwhile information about the quality and limiting parameters. N.c.a. Lu was confirmed to be superior for the preparation of radiolabeled compounds of high specific activity. Conclusions: For the first time we demonstrate that LCESI-TOF is a suitable tool for a direct species identification of Lu-radiolabeled peptides. Using a combination of different analytical approaches we could confirm that Lu is available with a high quality and can be used for an efficient preparation of therapeutic agents. Acknowledgements: We thank the team of Isotope and Elemental Analysis of Paul Scherrer Institute (Hot Laboratory Division/ Nuclear Energy and Safety Department) for the performance of SF-ICP-MS measurements.