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

201Tl is widely used in nuclear medicine to carry out myocardial perfusion imaging (MPI). 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 MPI, 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 200Tl, 201Tl and 202Tl 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 201Tl considered in ICRP publications 53 and 80 may be slightly underestimated.