A germanium-68/gallium-68 generator is a device used to extract the positron-emitting isotope 68Ga of gallium from a source of decaying germanium-68. The parent isotope68Ge has a half-life of 271 days and can be easily utilized for in-hospital production of generator produced 68Ga. Its decay product gallium-68 is extracted and used for certain positron emission tomographynuclear medicinediagnostic procedures, where the radioisotope's relatively short half-life and emission of positrons for creation of 3-dimensional PET scans, are useful.
The parent isotope germanium-68 is the longest-lived of the radioisotopes of germanium. It has been produced by several methods. In the U.S., it is primarily produced in proton accelerators: At Los Alamos National Laboratory, it may be separated out as a product of proton capture, after proton irradiation of Nb-encapsulated gallium metal. At Brookhaven National Laboratories, 40 MeV proton irradiation of a gallium metal target produces germanium-68 by proton capture and double neutron knockout, from gallium-69. This reaction is: 69Ga68Ge. A Russian source produces germanium-68 from accelerator-produced helium ion irradiation of zinc-66, again after knockout of two neutrons, in the nuclear reaction66Zn68Ge.
When loaded with the parent isotope germanium-68, these generators function similarly to technetium-99m generators, in both cases using a process similar to ion chromatography. The stationary phase is either metal-free or alumina, TiO2 or SnO2, onto which germanium-68 is adsorbed. The use of metal-free columns allows direct labeling of 68Ga without prepurification, hence making production of gallium-68-radiolabeled compounds more convenient. The mobile phase is a solvent able to elute gallium-68 after it has been produced by electron capture decay from the immobilized germanium-68. Currently, such 68Ga is easily eluted with a few mL of 0.05 M, 0.1 M or 1.0 M hydrochloric acid from generators using metal-free tin dioxide or titanium dioxide adsorbents, respectively, within 1 to 2 minutes. With generators of tin dioxide and titanium dioxide-based adsorbents, there remains more than an hour of pharmaceutical preparation to attach the gallium-68 as a tracer to the pharmaceutical molecules DOTATOC or DOTA-TATE, so that the total preparation time for the resulting radiopharmaceutical is typically longer than the 68Ga isotope half-life. This fact requires that these radiopharmaceuticals be made on-site in most cases, and the on-site generator is required to minimize the time losses.
Gallium-67 citrate salt imaging is useful for imaging old or sterile abscesses. Gallium-68 is useful in direct tumor imaging, especially leukocyte-derived malignancies and prostate cancermetastases.
