:Gallium-68 generator
{{Short description|A device used to extract the short-lived radioactive isotope Ga-68 from a longer-lived Ge-68 source}}
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 68Ga. 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 (<sup>68</sup>Ge) source
The parent isotope germanium-68 is the longest-lived (271 days) of the radioisotopes of germanium. It has been produced by several methods.{{Cite web |url=http://www.med.harvard.edu/JPNM/physics/isotopes/Ge/Ge68/prod.html |title=Note on Ge-68 production methods in 1996. Accessed March 15, 2010 |access-date=March 15, 2010 |archive-date=June 11, 2011 |archive-url=https://web.archive.org/web/20110611043400/http://www.med.harvard.edu/JPNM/physics/isotopes/Ge/Ge68/prod.html |url-status=dead }} 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.{{cite journal|last1=Bach|first1=H. T.|last2=Claytor|first2=T. N.|last3=Hunter|first3=J. F.|last4=Olivas|first4=E. R.|last5=Kelsey|first5=C. T.|last6=Connors|first6=M. A.|last7=Nortier|first7=F. M.|last8=Runde|first8=W. H.|last9=Modrell|first9=C.|last10=Lenz|first10=J. W.|last11=John|first11=K. D.|title=Improving the survivability of Nb-encapsulated Ga targets for the production of Ge-68|journal=Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms|date=15 March 2013|volume=299|pages=32–41|doi=10.1016/j.nimb.2013.01.035}} 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: 69Ga(p,2n)68Ge.
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 66Zn(α,2n)68Ge.
Mechanism of generator function
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 (wash out) gallium-68 (III) (68Ga3+) after it has been produced by electron capture decay from the immobilized (absorbed) germanium-68.
Currently, such 68Ga (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{{cite journal | last1 = Loc'h | first1 = C | last2 = Mazièré | first2 = B | last3 = Comar | first3 = D | title = A new generator for ionic gallium-68 | journal = Journal of Nuclear Medicine | volume = 21 | issue = 2 | pages = 171–3 | year = 1980 | pmid = 6965408 |name-list-style=vanc }} or titanium dioxide adsorbents, respectively, within 1 to 2 minutes. With generators of tin dioxide and titanium dioxide-based adsorbents, there once remained 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 68Ga isotope half-life. This fact required that these radiopharmaceuticals be made on-site in most cases, and the on-site generator is required to minimize the time losses. However, new kits such as "NETSPOT" for more rapidly preparing Ga-68 edotreotide or DOTATATE from Ga-68 (III) ions have increased the flexibility of sourcing of this radiopharmaceutical for Ga-68 endocrine receptor (octreotide) scans. With NETSPOT the preparation of the Ga-68 DOTATATE is immediate once the Ga-68 has been acquired from the generator and mixed with the reagent. {{Cite web|url=https://www.dmshealth.com/the-clinical-impact-of-utilizing-netspot/|title=The Clinical Impact of Utilizing NETSPOT - DMS Health|date=19 September 2019}}
Indications for gallium-68 PET scanning
{{main|Gallium scan}}
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 cancer metastases.
See also
References
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External links
- [https://web.archive.org/web/20110720032833/http://www2.mdanderson.org/app/techcommerc/body.cfm?mdaref=MDA04-016] M.D. Anderson article on automated synthesis of tracer molecules from gallium-68 in as little as 20 minutes, for PET scan uses.