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

Aim: Total thyroidectomy and risk-adapted 131-radioiodine therapy (RaIT) are the treatments of choice in differentiated thyroid cancer (DTC) patients. The response to treatments is assessed 6–12 months after RaIT. However, thyroglobulin (Tg) values obtained just before RaIT also provide reliable informations on patients'outcome. As available data were mostly obtained in hypothyroid status, we evaluated the predictive role of preablation-Tg in patients underwent RaIT after rhTSH stimulation. Material and methods: We enrolled 299 low-to-intermediate risk DTC patients underwent rhTSH-stimulated RaIT (standard protocol). Serum Tg levels were measured before rhTSH administration (basal Tg), before RaIT (early-stimulated Tg), and 2 days after RaIT (late-stimulated Tg). The early response assessment was done 12 months after RaIT according to 2015 American Thyroid Association (2015 ATA) criteria. Results: Most patients (277/299, 92.6%) had an excellent response (ER) to RaIT, while 15/299 (5.1%) and 7/299 (2.3%) patients showed biochemical incomplete/indeterminate response or persistent structural disease, respectively. At receiver operating characteristic analysis, the optimal cutoff to predict ER was set at 1.55 (AUC = 0.792), 2.6 (AUC = 0.931), and 4.9 (AUC = 0.874) ng/mL, for basal, early-, and late-stimulated Tg, respectively. The overall sensitivity, specificity, accuracy, positive predictive value (PPV), and negative predictive value (NPV) for basal, early-, and late-stimulated Tg were 50%, 96.7%, 93.3%, 55%, and 96.1%; 90.9%, 84.5%, 84.9%, 31.7%, and 99.1%; and 90.9%, 71.8%, 73.2%, 20.4%, and 99%, respectively. In univariate and multivariate logistic regression analysis, early-stimulated Tg cutoff resulted as an independent prognostic marker for predicting ER regardless of gender, age, histotype, histological variant, tumor size, risk classification, and stage of disease. Conclusion: Early-stimulated Tg is a reliable diagnostic tool for predicting the response to primary treatment of DTC. [ABSTRACT FROM AUTHOR]