Gallium-68-Generator

A Gallium-68 generator, also called 68Ge/68Ga-Generator is a nuclide to produce the radioactive 68Gallium3 ions from the radioactive also 68Germanium. The extracted from the generator 68Gallium used in nuclear medicine for the preparation of radiopharmaceuticals for positron emission tomography (PET).

68Gallium

The naturally occurring element gallium consists of two nonradioactive isotopes: 69Ga, which has a share of 60.1 % in natural gallium, and 71Ga, which forms the remaining 39.9%. All the other (ie, the non- naturally occurring gallium isotopes) are radioactive. The isotope 68Gallium decays with a half -life of only 67.629 minutes to 89% with the emission of a positron with a maximum of 1.9 MeV and 11% under electron; respectively in the stable isotope 68Zink. The - in 89 % of the decay cases - given positron has in nuclear medical application annihilate a range of only a few millimeters, then it encounters an electron and both elementary ( annihilate ) completely to form two photons, each with 511 keV (gamma radiation). The two photons are emitted while in an angle of nearly 180 ° apart from the place of destruction. The emitted photons can be detected with appropriate detectors and reconstruction of multiple detection events can be the place of Annihilation determine quite accurately. See the main article: positron emission tomography

68Gallium is perfectly suitable with its physical and chemical properties for nuclear medicine examinations. The short half-life fits well with the pharmacokinetics of many peptides to which it is bound in the diagnosis usually with the strong chelator DOTA. The complexation of gallium ions with DOTA is relatively simple and fast. On the other hand, makes the short half -life of 68 minutes a shipping or even a stocking this Isotopes almost impossible. This dilemma is solved with the 68Ge/68Ga-Generator.

Principle of 68Ge/68Ga-Generators

68Ge/68Ga-Generator in the required radionuclide 68Gallium is also generated from the radioactive 68Germanium. This isotope has a half -life of 270.8 days and decays by electron capture in the short-lived 68Gallium. In the generator, the germanium is bound to an insoluble matrix of an inert support (usually titanium ( IV) oxide ). The generator itself is 68Gallium by the continuous decay of germanium constantly formed, but which can not accumulate in large quantities by the significantly faster decay own. Is therefore formed in the generator a substantially constant concentration of produced ( generated ) 68Gallium ( 68Ge/68Ga-Gleichgewicht ). This amount of 68Gallium takes two events from:

• By eluting ( " milked " ) of the generator by means of a solvent in which it is soluble only 68Ga, 68Ge not.
• The slow decline of the 68Germanium content, due to its own decay.

In the first case the radioactive equilibrium between 68Ge/68Ga builds after each elution back to new. After a half time, ie 68 minutes, half the initial concentration is already reached. After two half-lives of three-quarters. Usually a waiting period of four to five hours until the next sampling is sufficient. The slow decay of 68Germanium causes the amount formed in each generator decreases continuously 68Gallium, after 270.8 days exactly in half. In practice, the used life of a 68Ge/68Ga-Generator is about one year.

Application

The 68Gallium generated in 68Ge/68Ga-Generator is used for a series of diagnostic studies using positron emission tomography. Most of these methods are, however, still in clinical testing. Most common is the assignment of Edotreotide ( DOTATOC ) with 68Gallium to 68Ga - DOTATOC.

Production

The 68Ge 68Ga used in generators is by irradiation of the stable isotope 69Gallium with accelerated protons (p, 2n ) were prepared.

Part of the generators is produced in Obninsk (Russia).

Perspective

Generally the 68Ge/68Ga-Generator prophesied a great future potential in clinical application. So far, however, the application is still limited to larger nuclear medicine centers. The big advantage over the other customary in PET isotopes, such as 18F, is that possible to dispense with complicated and expensive cyclotrons in the immediate vicinity.