Comparison of 1.1 GBq and 2.2 GBq Activities in Patients with Low-Risk Differentiated Thyroid Cancer Requiring Postoperative 131I Administration: A Real Life Study

The aim of the present study was to retrospectively evaluate the efficacy of low (1.1 GBq) versus moderate (2.2 GBq) I-131 activities in a large series (n = 299) of low-risk differentiated thyroid carcinoma (DTC) patients requiring postoperative I-131 ablation. At the follow-up, according to the ATA criteria, an excellent response was observed in 96.9% of patients treated with moderate I-131 activities versus 85.6% of patients treated with low I-131 activities (p = 0.029). Conversely, a biochemically indeterminate or incomplete response was observed in 22.2% of patients treated with low I-131 activities versus 1.8% of patients treated with moderate I-131 activities (p = 0.001), and an incomplete structural response was observed in three patients treated with low I-131 activities versus two patients treated with moderate I-131 activities (p = 0.654). In conclusion, we encourage the use of moderate instead of low activities when I-131 ablation is indicated in order to reach an excellent response in a significantly larger proportion of patients, including patients with the unexpected persistence of the disease.Objectives: To compare the efficacy of low and moderate I-131 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-131 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-131 activities, respectively (p = 0.029). A biochemically indeterminate or incomplete response was observed in seventeen (22.2%) patients treated with low I-131 activities and three (1.8%) patients treated with moderate I-131 activities (p = 0.001). Finally, five patients showed an incomplete structural response, among which three and two received low and moderate I-131 activities, respectively (p = 0.654). Conclusions: When I-131 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.