Pharmaceutical Manufacturing Handbook: Production and

PRODUCT MANUFACTURING 85
FIGURE 5 Small (less than 2 m in diameter) dual - beam negative ion cyclotron capable of
easily producing multicurie amounts of 18 F and 11 C. ( Photo courtesy of PET - CUN Center,
University of Navarra .)
It can easily be produced in very high quantities (up to 7 – 9 Ci per batch) even
in small cyclotrons with just a few hours irradiation time.
The mean positron emission energy of 18 F is just 0.64 MeV (the lowest of all
positron emitters with clinical use) and this has several important consequences:
The dose of radiation received by the patient will be lower and the
distance between disintegration of the radionuclide and the annihilation site
(after collision of the positron with an electron) is reduced, thus making PET
images with higher resolution possible.
The half - life of 18 F (109 min) is suffi ciently long to carry out complex synthesis
procedures, apply long PET imaging protocols, and carry out metabolite analysis.
Furthermore, it is possible to produce the radiopharmaceutical in a laboratory
and transport it to a distant site only equipped with an imaging device.
These kinds of “ satellite PET centers ” have boomed all around the world and
permitted the fast expansion of PET as an everyday clinical tool in certain
pathologies (mainly in oncological diseases).
Fluorine is not common in biological molecules, but many drugs contain this
atom. Fluorine and hydrogen have quite similar radii, and changing a hydrogen to
a fl uorine atom in a molecule does not usually generate substantial steric differences
between both molecules. Nonetheless, the electronegativity of fl uorine is usually