Characterization of radioiodine therapy failures in Graves' disease

Aim of this study was a characterization of radioiodine therapy (RIT) failu res in Graves' disease without simultaneous carbimazole. Method: 226 patien ts with a confirmed diagnosis of Graves' disease received 686.8 +/- 376.4 M Bq of iodine-131 orally for thyroid ablation. Target dose was 250 Gy. All p atients were followed up for 6 months. Therapy failures were compared with successes regarding possible influencing variables initial thyroid volume, thyroid function, immune activity (TRAb), 1-131 uptake, effective half-life , absorbed energy dose, age and gender. Results: 212 of 226 patients (93.8% ) were treated successfully, 14 (6.2%) showed a hyperthyroidism relapse wit hin 6 months which required a second radioiodine therapy. A success rate of 92.5% (62/67) could also be achieved with 67 patients who were hyperthyroi d at the time of RIT. Compared to the therapy successes, the 14 failures ac hieved significantly lower absorbed doses (223.8 +/- 76.6 Gy vs. 285.2 +/- 82.1 Gy, p <0.005), but with no significant differences regarding age, thyr oid volume, function or TRAb (all p >0.2). Of the 14 failures, n = 8 reache d on absorbed dose <200 Gy and n = 1 a dose <250 Gy, although 5 of the fail ures reached on absorbed dose of >250 Gy. Stepwise logistic regression reve aled only absorbed energy dose as a variable significantly influencing ther apy success (p <0.005), but no influence of initial thyroid volume, functio n, TRAb value, age (all p >0.2) or gender (p = 0.13). Two-tailed Fisher's e rect test showed no significant influence of gender on success rates (failu res/successes: male 1/36, female 13/176, p = 0.48). Conclusions: Except for the absorbed energy dose, no other significant variable influencing the ou tcome of radioiodine therapy in Graves' disease without simultaneous carbim azole could be found. It should be noted, though, that 5 therapy failures ( 2.2%) reached on absorbed energy dose of >250 Gy.