Comparison of 1.1 GBq and 2.2 GBq Activities in Patients with Low-Risk Differentiated Thyroid Cancer Requiring Postoperative I Administration: A Real Life Study.

[OBJECTIVES] To compare the efficacy of low and moderate I activities in low-risk differentiated thyroid carcinoma (DTC) patients requiring postoperative thyroid remnant ablation in a real-world clinical setting.

[METHODS] We retrospectively reviewed the records of 299 low-risk DTC patients (pT1-T2, Nx(0) Mx) who had undergone (near)-total thyroidectomy followed by I therapy, using either low (1.1 GBq) or moderate (2.2 GBq) radioiodine activities. The response to initial treatments was evaluated after 8-12 months, and patient responses were classified according to the 2015 American Thyroid Association guidelines.

[RESULTS] An excellent response was observed in 274/299 (91.6%) patients, specifically, in 119/139 (85.6%) and 155/160 (96.9%) patients treated with low and moderate I activities, respectively ( = 0.029). A biochemically indeterminate or incomplete response was observed in seventeen (22.2%) patients treated with low I activities and three (1.8%) patients treated with moderate I activities ( = 0.001). Finally, five patients showed an incomplete structural response, among which three and two received low and moderate I activities, respectively ( = 0.654).

[CONCLUSIONS] When I ablation is indicated, we encourage the use of moderate instead of low activities, in order to reach an excellent response in a significantly larger proportion of patients, including patients with the unexpected persistence of the disease.