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| Hauptseite > Publikationsdatenbank > Erzeugung von elementarem [$^{18}$F]Fluor mittels der $^{18}$O(p,n)$^{18}$F-Kernreaktion und Anwendung auf die $^{18}$F-Markierung aromatischer Aminosäuren |
| Dissertation / PhD Thesis/Book | PreJuSER-42492 |
2001
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
Jülich
Please use a persistent id in citations: http://hdl.handle.net/2128/19977
Report No.: Juel-3873
Abstract: Several aspects of production of the important PET-nuclide fluorine-18 (T$_{1/2}$ = 109,7 min, I$_{\beta+}$= 97 %) in the form of [$^{18}$F]F$_{2}$ via the $^{18}$O(p,n) $^{18}$F nuclear reaction were investigated. Special emphasis was placed on the development of the nuclear data base of the $^{18}$O(p,n) $^{18}$F reaction, on optimisation of the nuclide production techniques and on characterisation of the reaction products. [$^{18}$F]F$_{2}$ was then applied to the synthesis of the aromatic amino acids 2- [$^{18}$F]fluoro-L-tyrosine and 6-[$^{18}$F]fluoro-L-dopa. The excitation function of the $^{18}$O(p,n)$^{18}$F process was investigated from threshold to 30 MeV using the stacked-foil activation method. ${18}$F-activity was measured via $\gamma$-ray spectrometry and exact decay curve analysis. Irradiations were done at three different cyclotrons (E$_{p}$ = 4 - 30 MeV) and one VAN DE GRAAFF machine (E$_{p}$ < 4 MeV). As thin $^{18}$O-enriched targets commercially available $^{18}$O$_{2}$ and Si$^{18}$O$_{2}$ and electrochemically prepared Al$_{2}$$^{18}$O$_{3}$ were utilised. Considering the strong resonance structure of the excitation function only little activation data were available in the literature. In this work the gaps could be filled and the data base strengthened. The integral yield of fluorine-18 calculated from the new excitation curve is slightly higher than that from the hitherto accepted data set. Production of [$^{18}$F]F$_{2}$ was carried out via the known two step irradiation method using a reliable aluminium gas target. Under optimum conditions using 100 $\mu$mol F$_{2}$ a maximum [$^{18}$F]F$_{2}$- activity of 31 GBq and a specific radioactivity of 340 GBq/mmol (both 30 min after EOB) could be achieved. This is comparable to the best literature value. Higher specific activities up to 800 GBq/mmol could be achieved with less F$_{2}$ carrier. The total activity is then lower. The specific activity is 2.5 to 6 times higher than the specific activity of the [$^{18}$F]F$_{2}$ produced via the $^{20}$Ne(d,$\alpha$)$^{18}$F reaction. However, this specific radioactivity is not high enough for labelling receptor ligands. The [$^{18}$F]F$_{2}$ was radiochemically pure (> 99 %). The quality of the [$^{18}$F]F$_{2}$ produced was checked through the known synthesis of 6-[$^{18}$F]fluoro-L-dopa via fluorodestannylation. Final product activities (2.6 GBq) and the chemical yield (59.4 ± 4.6 %) were comparable to the literature values. Furthermore 2-[$^{18}$F]fluoro-L-tyrosine was synthesised for the first time via regioselective fluorodestannylation using [$^{18}$F]F$_{2}$. The compound 2-$\textit{tert}$-butyloxycarbonylamino-3-(4-$\textit{tert}$-butyloxycarbonyloxy-2-trimethylstannanylphenyl)-propionicacid ethyl ester was especially suitable for a fast radiosynthesis, because of the high fluorination yield and because the full deprotection of the functional groups could be carried out in one reaction step. About 1.7 GBq of the enantiomeric and isomeric pure product could be isolated. The yield of the total synthesis is about 17 times higher than that achieved by fluorodeprotonation of L-tyrosine. The activities of both tracers are high enough for performing several patient investigations as well as for transportation over relatively large distances.
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