Abstract
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Objectives: To compare production yields of 68Ga using different concentrations of 68Zn- nitrate, nitric acid, and irradiation parameters to optimize 68Ga production for routine application.
Methods: Different concentrations of 68Zn-nitrate (0.5 M and 1.0 M) in varying normality of nitric acid (0.8-1.5 N ) were prepared and irradiated with a proton beam on a low energy cyclotron (~14 MeV) using previously described1 BMLT-2 liquid target at different beam currents (20-45 µA) and irradiation time (30-60 min). The 68Ga production yields were calculated and compared with different irradiation conditions by decay correction of the produced activity at the end of the bombardment (EOB). 68Ga was isolated using in-house developed hydroxamate resin as described previously by Pandey et al.2-3 and optimized for routine application. Results: On increasing concentration of 68Zn-nitrate from 0.5 M to 1.0 M in 0.8 N nitric acid, decay corrected yield of 68Ga at EOB was found to be 2.06 GBq (55.6 mCi) and 3.34 GBq (90.3 mCi), respectively at 20 µA beam current, indicating production yield was proportional to zinc nitrate concentration. However, when beam current was increased to 30 µA while maintaining nitric acid concentration at 0.8 N, the proportional relationship of 68Zn-concentration with 68Ga production yield was lost (0.5 M, 2.96 GBq (80 mCi); 1.0 M, 3.92 GBq (106 mCi). Increasing nitric acid concentration to 1.25-1.5 N restored proportionality (1.0 M; 5.44GBq (147 mCi)). Similar studies were conducted to investigate the effects of beam current and duration of irradiation. Optimized yield of 3.69 GBq EOB was found for 0.5M 68Zn-nitrate in 0.8N HNO3, 30 min at 45 µA. MP-AES analysis showed <0.1 µg Ga (n=6), <10 µg Zn (n=6) and 0.6-8.0 µg Fe (n=6). Conclusions: 68Ga production yields were dependent on all four variables: concentration of 68Zn-nitrate, nitric acid concentration, beam current and duration of irradiation. Of note, increasing beam current and irradiation time may require increased concentrations of nitric acid to achieve expected increments in 68Ga yield. Research Support: This project was funded by Department of Energy, USA, GE Healthcare, and Department of Radiology, Mayo Clinic Rochester MN. References:
Pandey et al. Cyclotron production of 68Ga via the 68Zn (p, n) 68Ga reaction in aqueous solution American journal of nuclear medicine and molecular imaging 2014, 4 (4), 303
Pandey et al. WTTC 2016 Proceedings (http://wttc.triumf.ca): 10-11
Pandey et al. J Label Compd Radiopharma 2017, 60 (suppl.1) S111-S640, P388
Pandey et al. Automated Processing of Cyclotron Produced 68Ga Using Hydroxamate Resin Journal of Nuclear Medicine 2017, 58 (supplement 1), 333-333