201Tl-Thallium Chloride

Description

²⁰¹Tl-Thallium Chloride, also known as ²⁰¹Tl-Thallous Chloride, is a widely used radioactive salt. It plays a critical role in myocardial perfusion imaging (MPI), a diagnostic imaging technique that evaluates blood flow to the heart muscle.

Clinical Applications

1. Myocardial Perfusion Imaging (MPI):
²⁰¹Tl-Thallium Chloride is a valuable tool for diagnosing and localizing myocardial infarction (heart attack) and assessing ischemic heart disease, particularly atherosclerotic coronary artery disease.

2. Parathyroid Imaging:
Thallium helps localize sites of parathyroid hyperactivity in individuals with elevated serum calcium and parathyroid hormone levels, facilitating the diagnosis and treatment of conditions like hyperparathyroidism.

3. Breast Lesion Differentiation:
Research has demonstrated its utility in distinguishing benign from malignant breast lesions.

4. Lymphoma vs. Toxoplasmosis:
²⁰¹Tl is helpful in differentiating lymphoma from toxoplasmosis. Lymphoma typically shows strong thallium uptake, whereas toxoplasmosis exhibits mild uptake, aiding in precise diagnosis.

Dosage and Pharmacokinetics

• Typical Dosage: 3 to 4 mCi per imaging session.
• Biological Half-life: Approximately 10 days, making it less favorable than ^99mTc, which has a shorter half-life of 6.01 hours.
• Physical Half-life: 72.9 hours.

Availability and Cost

²⁰¹Tl-Thallium Chloride is produced by several leading radiopharmaceutical manufacturers globally. While some brands and products have been discontinued, others remain widely available:

• Manufacturers:
  • Lantheus (since 1977)
  • Mallinckrodt (since 1979)
  • Fuji Film
  • GE Healthcare (marketed as Thalsor, discontinued in 2005)
  • IBA Molecular (Curium)
  • Nihon Medi System
  • Trace Life

Cost:

• Approximately EUR 10–12 (US$ 11–13) per mCi.
• Typical patient dose: EUR 50 (US$ 55).
• In the USA, the average patient dose cost in 2020 was around US$ 170.

Competition

²⁰¹Tl-Thallium Chloride competes with ^99mTc-labeled MPI agents such as:

• ^99mTc-Sestamibi
• ^99mTc-Tetrofosmin

Preference for thallium or technetium tracers often depends more on physician familiarity with interpreting specific images than on demonstrable differences in diagnostic accuracy. During shortages of molybdenum-99 (⁹⁹Mo), the precursor for technetium-99m (^99mTc), thallium has been used as an effective alternative without major issues.

Comments on Usage Trends

The choice between ²⁰¹Tl and ^99mTc compounds for MPI is influenced by local practices, availability, and economic factors:

• US Trends: Centralized radiopharmacies and cost-reduction efforts have driven the adoption of ^99mTc-based tracers.
• European Trends: Early availability of ²⁰¹Tl contributed to its preference in Europe.
• Japanese Trends: High cyclotron deployment has led to alternatives like ¹³N or ¹⁵O, providing localized solutions.

Future Outlook

As the global use of ^99mTc-labeled compounds continues to rise, the market for ²⁰¹Tl is expected to diminish. However, any future developments in myocardial tracers must consider regional differences in medical practices and economic factors to ensure widespread adoption.

Both ²⁰¹Tl and ^99mTc-labeled tracers offer reliable diagnostic capabilities, enabling cardiologists to make accurate assessments based on their specific clinical requirements.