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Thallous Chloride Tl-201 Injection
Thallous Chloride Tl-201 Injection (thallous chloride)
Diagnostic – For Intravenous Use
Thallous Chloride Tl-201 Injection (thallous chloride) is supplied in an isotonic solution as a sterile, non-pyrogenic diagnostic radiopharmaceutical for intravenous administration. Each milliliter contains 37 megabecquerels (1 millicurie) Thallous Chloride Tl-201 at calibration time, made isotonic with 9 milligrams sodium chloride and preserved with 0.9% (v/v) benzyl alcohol. The pH is adjusted to between 4.5 to 7.0 with hydrochloric acid and/or sodium hydroxide. Thallium Tl-201 is cyclotron produced. At the time of calibration it contains no more than 1.0% Thallium Tl-200, no more than 1.0% Thallium Tl-202, no more than 0.25% Lead Pb-203, and no less than 98% Thallium Tl-201 as a percentage of total activity. No carrier has been added.
It is recommended that Thallous Chloride Tl-201 be administered close to calibration time to minimize the effect of higher levels of radionuclidic contaminants present at pre- and post-calibration dates. The concentration of each radionuclidic contaminant changes with time. Figure 1 shows maximum concentration of each radionuclidic contaminant as a function of time.
Figure 1. Radionuclidic Contaminants
Thallium Tl-201, with a physical half life of 73.1 hours, decays by electron capture to mercury Hg 201.1 Photons that are useful for detection and imaging are listed in Table 1. The lower energy x-rays obtained from the mercury Hg 201 daughter of thallium Tl-201 are recommended for myocardial imaging, because the mean percent disintegration at 68.9 to 80.3 keV is much greater than the combination of gamma-4 and gamma-6 mean percent disintegration.
Table 1. Principal Radiation Emission Data
|Radiation||MeanPercent/ Disintegration||Energy (keV)|
The specific gamma ray constant for thallium Tl-201 is 4.7 R/mCi-hr2 at 1 cm. The first half-value thickness of lead (Pb) is 0.0006 cm. A range of values for the radiation emitted by this radionuclide with the corresponding exposure rate at 1 cm that results from interposition of various thicknesses of lead is shown in Table 2. For example, the use of 0.21 cm of lead will decrease the external radiation exposure by a factor of about 1,000.
Table 2. Radiation Attenuation by Lead Shielding
|cm of Lead(Pb)||Coefficient of Attenuation|
To correct for physical decay of the radionuclide, the fractions that remain at selected intervals after calibration time are shown in Table 3.
Table 3. Thallium Tl-201 Decay Chart; Half-Life 73.1 Hours
|Hours||Fraction Remaining||Hours||Fraction Remaining|
1. Kocher, David C., "Radioactive Decay Data Tables," DOE/TIC- 11026, 181 (1981).
2. Includes 10 keV x-rays.
Last reviewed on RxList: 10/21/2008
This monograph has been modified to include the generic and brand name in many instances.
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