A 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 isotope 68Ge has a half-life of 271 days and can be easily sent to hospitals within the generator, where it is storable for almost a year. Its decay product gallium-68 (with a half-life of only 68 minutes, inconvenient for transport) is extracted and used for certain positron emission tomography nuclear medicine diagnostic procedures, where the radioisotope's relatively short half-life and emission of positrons for creation of 3-dimensional PET scans, are useful.
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The parent isotope germanium-68 is the longest-lived (271 days) of the radioisotopes of germanium. It has been produced by several methods.[1] In the U.S., it is primarily produced in proton accelerators: At Los Alamos National Laboratory, it may be separated out as a spallation product, after proton irradiation of molybdenum or rubidium. 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 (the most common of two stable isotopes of gallium). This reaction is: Ga-69 + p --> 2n + Ge-68.
A Russian source produces germanium-68 from accelerator-produced helium ion (alpha) irradiation of zinc-66, again after knockout of two neutrons, in the nuclear reaction Zn-66 + alpha --> 2n + Ge-68.
When loaded with the parent isotope germanium-68, these generators function similarly to technetium-99m generators, in both cases using a process similar to thin layer chromatography. The stationary phase is alumina, TiO2 or SnO2, onto which germanium-68 is adsorbed. The mobile phase is a solvent able to elute (wash out) decayed germanium-68, after it has decayed by electron capture to gallium-68 (III) ( 68Ga3+).[2]
Currently Ga-68 (III) is easily eluted with a few mL of 1.0 M or 0.1 M hydrochloric acid from generators with tin dioxide [3] or titanium dioxide adsorbents, respectively, within 1 to 2 minutes. With the generators of tin dioxide and titanium dioxide based adsorbents there remains more than an hour of pharmaceutical preparation to attach the gallium-68 (III) as a tracer to the pharamaceutical molecules DOTATOC or DOTA-TATE, so that the total preparation time for the resulting radiopharmaceutical is typically longer than the Ga-68 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.