Abstract: [Background] Positron emission tomography/computed tomography (PET/CT) is a routine diagnostic method of particular importance for treatment evaluation and management in oncology. It is very important for PET/CT diagnosis to produce good quality and quantity positron nuclides using medical cyclotron. [Purpose] The effect of irradiation conditions and bombardment parameters on positron nuclide ¹⁸F production was analyzed to acquire the optimized production conditions and optimum bombardment parameters. [Methods] Origin 9.0 software was used to analyze the change of ¹⁸F yield with different proton beam current and bombardment time. Monte Carlo method was applied to establish the target chamber model of proton irradiation, and the proton energy, thicknesses of Havar foils and the ¹⁸O water were analyzed to obtain the optimum conditions of beam current, bombardment time and the proton energy, etc. [Results] Proton beam should thoroughly irradiate on target chamber center to make the best of beam current for triggering as much as nuclear reaction. When 20-MeV proton beam was used to produce ¹⁸F, the thicknesses of Havar foil and the target water were recommended to be 60 μm and 3 mm, respectively. Usually, the yield of ¹⁸F increases with the beam current. The longer the bombardment time was, the higher the yield of ¹⁸F. But with bombardment time increased, the trend of yield became slower. The bombardment time was suggested approximately 60 min. [Conclusion] It is necessary to select the appropriate thicknesses of Havar foil and the ¹⁸O water for positron radionuclide ¹⁸F production (this paper shows that the thicknesses of Havar foil and the ¹⁸O water should be 60 μm and 3 mm when the proton energy is 20 MeV). The irradiation time was suggested approximate 60min to obtain high yield of ¹⁸F. Furthermore, irradiation should be started after the cyclotron run for a period of time for stabilization.

Key words: Cyclotron, Proton, ¹⁸F, Production conditions, Monte Carlo method