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 11 C-, 15 O-, or 18 F-labeled tracers produced from gaseous materials via chemical reactions had no radionuclidic impurities, whereas 18 F-FDG, 18 F-NaF, and 13 N-NH3 produced from aqueous materials had several γ-emitters as well as impure positron emitters. 15 O-Labeled CO2 , O2 , and CO had a radionuclidic impurity 13 N-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 15 O-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.