fluoroestradiol f 18 - Medications

11.1 Chemical Characteristics CERIANNA contains fluoroestradiol fluorine 18 (F 18), a synthetic estrogen analog. Chemically, fluoroestradiol F 18 is [18F]16α-fluoro-3,17β-diol-estratriene-1,3,5(10). The molecular weight is 289.37, and the structural formula is: CERIANNA is a sterile, clear, colorless solution for intravenous injection, with an osmolarity of 340 mOsm. Its pH ranges between 5.5 to 8.0. The composition of the final product in 40 mL solution is fluoroestradiol no more than 5 mcg, fluoroestradiol F 18 148 MBq/mL to 3,700 MBq/mL (4 mCi/mL to 100 mCi/mL), sodium ascorbate 0.44% w/v in sodium chloride 0.9% w/v, and ethanol no more than 3.2% w/v. Chemical Structure 11.2 Physical Characteristics CERIANNA is radiolabeled with F 18, a cyclotron produced radionuclide that decays by positron emission to stable oxygen 18 with a half-life of 109.8 minutes. The principal photons useful for diagnostic imaging are the coincident pair of 511 keV gamma photons, resulting from the interaction of the emitted positron with an electron (Table 2). Table 2. Principal Radiation Produced From Decay of Fluorine 18 Radiation Radiation Energy Level (keV) % Abundance Positron 249.8 96.9 Gamma 511 193.5 11.3 External Radiation The point source air-kerma coefficient for F 18 is 3.75 × 10 -17 Gy m 2 / (Bq s). The first half-value thickness of lead (Pb) for F 18 gamma rays is approximately 6 mm. The relative reduction of radiation emitted by F 18 that results from various thicknesses of lead shielding is shown in Table 3. The use of 8 cm Pb decreases the radiation transmission (i.e., exposure) by a factor of about 10,000. Table 3. Radiation Attenuation of 511 keV Gamma Rays by Lead Shielding Shield Thickness cm of Lead (Pb) Coefficient of Attenuation 0.6 0.5 2 0.1 4 0.01 6 0.001 8 0.0001