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

OBJECTIVE To elucidate the radionuclides and radiochemical impurities included in radiosynthesis processes of positron emission tomography (PET) tracers. METHODS 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. RESULTS 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 %). CONCLUSIONS 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.