Gallium Citrate Ga-67

DESCRIPTION Gallium Citrate Ga 67 Injection is supplied in a 10 milliliter vial as an isotonic, sterile, non-pyrogenic solution. Each milliliter of the isotonic solution contains 74 megabecquerels (2 millicuries) of gallium Ga-67 on the calibration date as a complex formed from 8.3 nanograms gallium chloride Ga-67, 1.9 milligrams of sodium citrate dihydrate, 7.8 milligrams of sodium chloride and 0.9 percent benzyl alcohol (v/v) as a preservative. The pH is adjusted to between 5.5 to 8.0 with hydrochloric acid and/or sodium hydroxide solution. Gallium Ga-67, with a half-life of 78.26 hours, is cyclotron produced by the proton irradiation of enriched zinc. At the time of calibration the drug contains no more than 0.02% gallium Ga-66 and no more than 0.2% zinc Zn-65. The concentration of each radionuclidic impurity changes with time. At expiration, the drug contains no more than 0.001% gallium Ga-66 and no more than 1.0% zinc Zn-65. No carrier has been added. Gallium citrate has the following chemical structure: P hysical Characteristics Gallium Ga-67 with a physical half-life of 78.26 hours 1 decays by electron capture to stable zinc Zn-67. Photons that are useful for imaging studies are listed in Table 1. Table 1. Principal Radiation Emission Data Radiation Mean Percent Per Disintegration Energy (keV) Gamma-2 Gamma-3 Gamma-4 Gamma-5 Gamma-6 Gamma-7 2.9 35.7 19.7 2.2 16.0 4.5 91.3 93.3 184.6 209.0 300.2 393.5 1 Kocher, D.C., Radioactive Decay Data Tables, Health and Safety Research Division, National Technical Information Service, DOE/TIC-11026, pg. 80, 1981. E xternal Radiation The specific gamma ray constant for gallium Ga-67 is 1.6 R/mCi-hour at 1 cm. The first half-value thickness of lead (Pb) is 0.066 cm. A range of values for the relative attenuation of the radiation emitted by this radionuclide that results from interposition of various thicknesses of lead is shown in Table 2. For example, the use of 1.2 cm of lead will decrease the radiation exposure by a factor of about 100. Table 2. Radiation Attenuation by Lead Shielding Shield Thickness (Pb), cm Coefficient of Attenuation 0.066 0.41 1.2 2.5 4.8 0.5 10 - 1 10 - 2 10 - 3 10 - 4 To correct for physical decay of this radionuclide, the fractions that remain at selected time intervals after the time of calibration are shown in Table 3. Table 3. Physical Decay Chart; Gallium Ga-67, Half-Life 78.26 Hours Hours Fraction Remaining Hours Fraction Remaining 0* 6 12 18 24 (1d) 30 36 42 48 (2d) 54 60 66 1.000 0.948 0.899 0.853 0.809 0.767 0.727 0.689 0.654 0.620 0.588 0.557 72 (3d) 78 84 90 96 (4d) 108 120 (5d) 132 144 (6d) 156 168 (7d) 0.529 0.501 0.475 0.451 0.427 0.384 0.345 0.311 0.279 0.251 0.226 * Calibration Time Gallium citrate chemical structure