Production of [18F]F2 Gas for Electrophilic Substitution Reaction

Moon, Byung Seok; Kim, Jae Hong; Lee, Kyo Chul; An, Gwang Il; Cheon, Gi Jeong; Chun, Kwon Soo

Abstract

PURPOSE: Electrophilic 18F (T1/2=110 min) radionuclide in the form of [18F]F2 gas is of great significance for labeling radiopharmaceuticals for positron emission tomography (PET). However, its production in high yield and with high specific radioactivity is still a challenge to overcome several problems on targetry. The aim of the present study was to develop a method suitable for the routine production of [18F]F2 for the electrophilic substitution reaction.
MATERIALS AND METHODS
The target was designed water-cooled aluminum target chamber system with a conical bore shape. Production of the elemental fluorine was carried out via the 18O(p,n)18F reaction using a two-step irradiation protocol. In the first irradiation, the target filled with highly enriched 18O2 was irradiated with protons for 18F production, which were adsorbed on the inner surface of target body. In the second irradiation, the mixed gas (1% [19F]F2/Ar) was loaded into the target chamber, following a short irradiation of proton for isotopic exchange between the carrier-fluorine and the radiofluorine absorbed in the target chamber. Optimization of production was performed as the function of irradiation time, the beam current and 18O2 loading pressure.
RESULTS
Production runs was performed under the following optimum conditions: The 1st irradiation for the nuclear reaction (15.0 bar of 97 % enriched 18O2, 13.2 MeV protons, 30 micro A, 60-90 min irradiation), the recovery of enriched oxygen via cryogenic pumping; The 2nd irradiation for the recovery of absorbed radiofluorine (12.0 bar of 1% [19F]fluorine/argon gas, 13.2 MeV protons, 30 micro A, 20-30 min irradiation), the recovery of [18F]fluorine for synthesis. The yield of [18F]fluorine at EOB (end of bombardment) was achieved around 34+/-6.0 GBq (n>10).
CONCLUSION
The production of 18F electrophilic agent via 18O(p,n)18F reaction was much under investigation. Especially, an aluminum gas target was very advantageous for routine production of [18F]fluorine. These results suggest the possibility to use [18F]F2 gas as a electrophilic substitution agent.