In the last 5 years the number of PET investigations had raised nearly tenfold, this year it is near to 12000. In the procedures [18F]FDG (2-[18F]fluoro-2-deoxy-D-glucose) is used in nearly 100 %. The use of a few times C-11 labelled methionine and acetate besides the FDG is negligible. In our country the technical conditions of PET radiopharmaceutical production are excellent. Two laboratories obtained production licence, and marketing authorizations for FDG and the above mentioned C-11 tracers. This makes possible to provide FDG not only for Hungary, but for the neighbouring countries (Romania, Serbia, Bulgaria) as well. The registered C-11 labelled tracers are used on the spot. In Debrecen the process of registration of C-11 labelled choline has been started.

Aim: The radiochemical purity of [18F]FDG at high radioactive concentrations decreases in time rapidly due to active species formed during the radiolysis of water. In this study we intended to clarify the effect of selective scavengers of hydroxyl radicals and hydrated electrons on the stability of [18F]FDG. Our goal was also to examine the stabilization effect of various salts, B-vitamins, sugars and amino acids, which are effective hydroxyl radical scavengers.

Materials & methods: We studied the impact of stabilizers using 50-100 μL of samples of [18F]FDG treated with reagents to the concentrations of 50 mmol/L. The initial radioactive concentrations of samples were approximately 2 GBq/ml. Both treated and untreated [18F]FDG samples were stored at room temperature (25°C). Stability was tested by analyzing the samples at appropriate time intervals. We determined the radiochemical purity of [18F]FDG samples by thin layer chromatography method: Merck TLC Silica gel 60, acetonitrile/water 95/5V/V%, 18F Rf=0, [18F]FDG Rf=0.45, Acetyl-[18F]FDG Rf=0.65.

Results: We found that the radiochemical purity of the untreated [18F]FDG sample after 210 minutes decreased to 94.70%. In the presence of ammonium formate (selective hydroxyl radical scavenger) and sodium nitrate (selective scavenger of hydrated electrons) the radiochemical purities were 96,76% and 95,35%, respectively. On the other hand the [18F]FDG sample treated with the mixture of formate and nitrate had a purity of 96,13%. Consequently, selective hydroxyl radical scavengers are the most effective stabilizers for [18F]FDG. We also investigated the relationship between the effectiveness of stabilizers and the rate constants of their reactions with hydroxyl radicals (kOH). We found that the purity of samples treated with selective OH scavengers, namely with potassium iodide (kOH: 1.1∙1010 L∙mol-1∙s-1), ethanol (kOH: 1.9∙109 L∙mol-1∙s-1) and sodium acetate (kOH: 7.4∙107 L∙mol-1∙s-1) were 98,90%, 98,74% and 97,96%, respectively. Consequently, the higher the kOH of the stabilizer the more effective for stabilizing [18F]FDG. In addition we found that several OH radical scavengers effectively suppress the radiolytic decomposition of [18F]FDG. For instance, the purity of samples treated with glucose, thiamine and methionine decreased with 1,5%.

Conclusion: Selective OH scavengers with high kOH should be chosen to effectively stabilize [18F]FDG against radiolysis. Among the examined stabilizers glucose could be ideal, as it meets the above mentioned requirements and there is no need for a new analytical method for its quantification, since the HPLC method recommended by the Ph. Eur.6.2 for the determination of radiochemical purity of [18F]FDG can be used for this purpose.