Gallium-68 generator

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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 isotope 68Ge has a half-life of 271 days and can be easily utilized for in-hospital production of generator produced Ga-68. 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.

Parent isotope (Ge-68) source[edit]

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 product of proton capture, after proton irradiation of Nb-encapsulated gallium metal.[2] 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(α,2n)Ge-68.

Mechanism of generator function[edit]

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 Ga-68 without prepurification, hence making production of gallium-68-radiolabeled compounds more convenient. The mobile phase is a solvent able to elute (wash out) gallium-68 (III) (68Ga3+) after it has been produced by electron capture decay from the immobilized (absorbed) germanium-68.

Currently, such Ga-68 (III) 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 [3] 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 (III) 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 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.

Indications for gallium-68 PET scanning[edit]

For the types of medical problems usefully imaged by Gallium-68 PET, see gallium-67 scan, in which a different radioisotope of gallium is used, but one that has exactly the same localization characteristics in the body, and therefore shows the same pathological processes. Gallium radioisotope imaging is useful for imaging old or sterile abscesses, and also can be useful in direct tumor imaging, especially leukocyte-derived malignancies.

See also[edit]

References[edit]

  1. ^ Note on Ge-68 production methods in 1996. Accessed March 15, 2010
  2. ^ Bach, H. T.; Claytor, T. N.; Hunter, J. F.; Olivas, E. R.; Kelsey, C. T.; Connors, M. A.; Nortier, F. M.; Runde, W. H.; Modrell, C.; Lenz, J. W.; John, K. D. (15 March 2013). "Improving the survivability of Nb-encapsulated Ga targets for the production of Ge-68". Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms. 299: 32–41. 
  3. ^ Loc'h C, Mazièré B, Comar D (1980). "A new generator for ionic gallium-68". Journal of Nuclear Medicine. 21 (2): 171–3. PMID 6965408. 

External links[edit]

  • [1] M.D. Anderson article on automated synthesis of tracer molecules from gallium-68 in as little as 20 minutes, for PET scan uses.