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.

Automated summary

The aim of this study was to compare the efficacy of low (1.1 GBq) versus moderate (2.2 GBq) I-131 activities in low-risk differentiated thyroid carcinoma (DTC) patients requiring postoperative thyroid remnant ablation. The results showed that moderate I-131 activities led to a significantly higher proportion of patients with an excellent response compared to low I-131 activities (p = 0.029). Conversely, low I-131 activities were associated with a higher proportion of patients with a biochemically indeterminate or incomplete response (p = 0.001). Therefore, the use of moderate activities is encouraged to achieve better treatment outcomes.