Determination of radionuclides and radiochemical impurities produced by in-house cyclotron irradiation and subsequent radiosynthesis of PET tracers

To elucidate the radionuclides and radiochemical impurities included in radiosynthesis processes of positron emission tomography (PET) tracers. Target materials and PET tracers were produced using a cyclotron/synthesis system from Sumitomo Heavy Industry. Positron and γ-ray emitting radionuclides were quantified by measuring radioactivity decay and using the high-purity Ge detector, respectively. Radiochemical species in gaseous and aqueous target materials were analyzed by gas and ion chromatography, respectively. Target materials had considerable levels of several positron emitters in addition to the positron of interest, and in the case of aqueous target materials extremely low levels of many γ-emitters. Five ¹¹C-, ¹⁵O-, or ¹⁸F-labeled tracers produced from gaseous materials via chemical reactions had no radionuclidic impurities, whereas ¹⁸F-FDG, ¹⁸F-NaF, and ¹³N-NH₃ produced from aqueous materials had several γ-emitters as well as impure positron emitters. ¹⁵O-Labeled CO₂, O₂, and CO had a radionuclidic impurity ¹³N-N₂ (0.5-0.7%). Target materials had several positron emitters other than the positron of interest, and extremely low level γ-emitters in the case of aqueous materials. PET tracers produced from gaseous materials except for ¹⁵O-labeled gases had no impure radionuclides, whereas those derived from aqueous materials contained acceptable levels of impure positron emitters and extremely low levels of several γ-emitters. (author)