Gallium-68 generator
Encyclopedia
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.
, 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.
s, 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+).
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 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.
Gallium
Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies...
from a source of decaying germanium-68. The parent isotope 68Ge has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
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
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
nuclear medicine
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
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
The parent isotope germanium-68 is the longest-lived (271 days) 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 LaboratoryLos Alamos National Laboratory
Los Alamos National Laboratory is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico...
, 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.
Mechanism of generator function
When loaded with the parent isotope germanium-68, these generators function similarly to technetium-99m generatorTechnetium-99m generator
A technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a source of decaying molybdenum-99...
s, in both cases using a process similar to thin layer chromatography
Thin layer chromatography
Thin layer chromatography is a chromatography technique used to separate mixtures. Thin layer chromatography is performed on a sheet of glass, plastic, or aluminum foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose...
. 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+).
Currently Ga-68 (III) is easily eluted with a few mL of 1.0 M or 0.1 M hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
from generators with tin dioxide 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
DOTA-TATE
DOTA-TATE, DOTATATE or DOTA-octreotate is a substance which, when bound to various radionuclides, has been tested for the treatment and diagnosis of certain types of cancer, mainly neuroendocrine tumours.-Chemistry and mechanism of action:...
, 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.
See also
- Isotopes of germaniumIsotopes of germaniumGermanium has five naturally occurring isotopes, 70Ge, 72Ge, 73Ge, 74Ge, and 76Ge. Of these, 76Ge is very slightly radioactive, decaying by double beta decay with a half-life of 1.78 × 1021 years , giving it the distinction of being the nuclide with the longest directly measured...
- Positron emission tomographyPositron emission tomographyPositron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
- Technetium-99m generatorTechnetium-99m generatorA technetium-99m generator, or colloquially a technetium cow or moly cow, is a device used to extract the metastable isotope 99mTc of technetium from a source of decaying molybdenum-99...
External links
- 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.