Thyroid remnant ablation with radioiodine activity of 30, 60, and 100 mCi in patients with differentiated thyroid cancer - a prospective comparison of long-term outcomes.

Introduction: The aim of this prospective study was to evaluate long-term outcomes in differentiated thyroid cancer (DTC) patients postoperatively treated with distinct RAI activities of 30 mCi, 60 mCi, and 100 mCi. Material and methods: The analysis involved 277 low-risk and 46 intermediate-risk patients, who underwent radioiodine (RAI) ablation with 30 mCi, 60 mCi or 100 mCi under prospective, randomized clinical trials. Seventy-eight patients from the low-risk group received 30 mCi, whereas 125 and 74 patients received 60 mCi and 100 mCi, respectively. Regarding the intermediate-risk group, 20 patients were given 60 mCi, and 26 subjects were given 100 mCi. The mean time of follow-up was 11 years. Results: An excellent treatment response was obtained in 88%, 89% and 90% of low-risk patients treated with 30 mCi, 60 mCi, and 100 mCi, respectively, and in 85% of intermediate-risk patients, who were administered 60 or 100 mCi. An indeterminate response was achieved in 9.4% and 6.5%, whereas an incomplete structural response was obtained in 1.4% and 6.5% of low-risk and intermediate-risk patients, respectively. An incomplete biochemical response was observed only in 2.2% of intermediate-risk patients. The differences in treatment response regarding RAI activity were not significant. Conclusions: RAI activity of 30 mCi demonstrates a comparable efficacy as 60 mCi and 100 mCi in low-risk DTC. RAI activity of 60 mCi seems to be effective in intermediate-risk DTC.