[The effective half-life of 131I during the treatment of autonomous thyroid disease with radioiodine].

In order to compute effective half-life of 131I after application of therapeutic doses (Teff), the time course of whole-body radioactivity was evaluated retrospectively in 115 patients with benign thyroid diseases (multinodular autonomous adenoma, solitary autonomous adenoma or Graves' disease). Because of a large overlap of Teff in the various diseases analyzed, courses of all patients who did (group Ts, 24 cases) or did not (group kTs, 91 cases) receive antithyroid drugs during therapy were summarized. In group Ts a mean Teff of 5.0 +/- 0.9 d was found which was significantly (p less than 0.01) lower than the mean Teff of 6.3 +/- 0.9 d in group kTs. We believe that the mean Teff is a practical alternative in radioiodine dosimetry if an exact determination of Teff cannot be performed because of shortage of time.