Long term retention and excretion of 201Tl in a patient after myocardial perfusion imaging.

Tl-201 is widely used in nuclear medicine to carry out myocardial perfusion imaging (NIPI). However, very limited data is available on long-term distribution in the body, excretion and corresponding dose. In this study we performed a 2 month follow-up of a patient who underwent NIPI, by urine analysis and in vivo measurements. The biological half-life of thallium was consequently estimated to be 11.6-27 d, which is in partial agreement with previous studies. We also estimated excretion and retention of Tl-200, Tl-201 and Tl-202 isotopes using the biokinetic parameters from ICRP publication 53 and compared the forecast result with actual measurements. The latter demonstrated a higher urinary excretion and a higher body retention than what was expected. Our results therefore suggest that the long-term retention and consequently the effective dose coefficient for Tl-201 considered in ICRP publications 53 and 80 may be slightly underestimated.