title: Characterization of SnO2-based (68)Ge/ (68)Ga generators and (68)Ga-DOTATATE preparations: radionuclide purity, radiochemical yield and long-term constancy.
abstract: BACKGROUND
  With the increasing utilization of (68)Ge-(68)Ga radionuclide generators, (68)Ga labelled peptides like DOTATATE are receiving more attention in nuclear medicine. On the one hand, the long half-life of the parent nuclide (68)Ge is an enormous advantage for routine applications, but the question of the long-term stability of the (68)Ge breakthrough arises, which up to now has scarcely been investigated.
  
  
  METHODS
  A sum of 123 eluates from four different (68)Ge-(68)Ga generators (iThemba Labs, Faure, South Africa) and 115 samples of the prepared radiopharmaceutical (68)Ga-DOTATATE were measured first with a dose calibrator and again after decay of the eluted (68)Ga via gamma-ray spectrometry. A complete decay curve was recorded for one sample eluate. A further three eluates were eluted in ten fractions of 0.5 ml in order to obtain detailed information concerning the distribution of the two nuclides within the eluates. The influences of factors such as the amount of DOTATATE, addition of Fe(3+) salts and replacement of HEPES buffer with sodium acetate on the radiochemical synthesis were also tested.
  
  
  RESULTS
  The content of long-lived (68)Ge breakthrough increases over the entire period of use to more than 100 ppm. The labelling process with the chelator DOTA removes (68)Ge efficiently. The maximum activity found in the residues of the radiopharmaceuticals investigated in this study was below 10 Bq in nearly all cases. In many cases (12% of the labelled substance), the long-lived parent nuclide could not be identified at all. The labelling process is still viable for reduced amounts of the chelator and with acetate buffer.
  
  
  CONCLUSIONS
  Effective doses received by the patient from (68)Ge in the injected radiopharmaceutical (68)Ga-DOTATATE are lower than 0.1 μSv and are therefore practically negligible, especially when compared with the contribution of the PET radiopharmaceutical itself. Gamma-ray spectrometry as recommended by the European Pharmacopeia is suitable for quantification of radionuclidic impurities.
authors.affiliation: Department of Nuclear Medicine, University Hospital of Cologne, Kerpener Str 62, Cologne, NRW 50937, Germany, Ferdinand.Sudbrock@uk-koeln.de.
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Sudbrock
authors.forename: Thomas
authors.initials: T
authors.lastname: Fischer
authors.forename: Beate
authors.initials: B
authors.lastname: Zimmermanns
authors.forename: Mehrab
authors.initials: M
authors.lastname: Guliyev
authors.forename: Markus
authors.initials: M
authors.lastname: Dietlein
authors.forename: Alexander
authors.initials: A
authors.lastname: Drzezga
authors.forename: Klaus
authors.initials: K
authors.lastname: Schomäcker