Kinetics and dosimetry of thallium-201 in human testes

Thallous chloride (²⁰¹Tl) is a well-known imaging agent. It has been shown to accumulate in the testes. In view of this, the testicular kinetics of ²⁰¹Tl is investigated in humans and the absorbed dose to the organ calculated. Methods: Thallous chloride ²⁰¹Tl was injected intravenously into four patients for myocardial perfusion studies. After clinical evaluation, the testicular uptake and clearance of ²⁰¹Tl were monitored for about 1 wk using a gamma camera. Results: Testicular uptake of ²⁰¹Tl was rapid with a mean biological uptake half-time of 0.67 hr and mean biological clearance half-time of 280 hr. The mean maximum testicular uptake of ²⁰¹Tl was about 0.4% of the injected activity. These data were utilized to calculate the average absorbed dose to the testes. The absorbed dose to the testes was calculated to be 3.5 x 10^-4 Gy/MBq (1.3 rad/mCi) of injected activity. Conclusion: When the relative biological effectiveness of the Auger emitter ²⁰¹Tl is taken into account, the equivalent dose to the testes is 9.5 x 10^-4 Sv/MBq (3.5 rem/mCi).