Relationship between circulating anti-thyroglobulin antibodies (TgAb) and tumor metabolism in patients with differentiated thyroid cancer (DTC): prognostic implications.

PURPOSE: TgAb have been proposed as tumor markers in DTC. Recent evidence links TgAb levels with DTC aggressiveness. We aimed to evaluate the relationship between TgAb and tumor glucose metabolism in DTC patients. METHODS: Seventy-one DTC patients who underwent 18F-FDG PET/CT were included. According to TgAb value and trends, patients were divided into TgAb positive (TgAb+) or negative (TgAb-) as well as in patients with increasing (Inc-TgAb) or decreasing (Dec-TgAb) trend. On the basis of the results of FDG-PET, post-therapy 131I and Tg levels, patients were divided into two groups according to the evidence (ED) or absence (NED) of disease. ED patients were further divided into three subgroups: 1. radioiodine avid with positive 18F-FDG PET/CT (PET+/131I+), 2. radioiodine refractory with positive 18F-FDG PET/CT (PET+/131I-) and 3. radioiodine avid with negative 18F-FDG PET/CT (PET-/131I+). MeanSUV of FDG-avid lesions was assessed and averaged for each patient (SUVmean-pt). T test was performed to assess the difference between SUVmean in TgAb-, TgAb+ and in Inc-TgAb and Dec-TgAb subgroups. Difference in TgAb between ED and NED patients as well as between ED patients and PET+/131I+, PET+/131I- and PET-/131I+ subgroups was compared. RESULTS: SUVmean was significantly higher in Inc-TgAb with respect to Dec-TgAb subgroup (5.2 ± 1.5 vs. 2.9 ± 1.1, p < 0.05). TgAb were higher only in the ED PET+/131I+ subgroup with respect to NED patients (p < 0.01). CONCLUSIONS: The relationship between higher tumor metabolism and trend of TgAb supports a prognostic relevance of TgAb in DTC patients. Significantly higher TgAb in radioiodine avid tumors with positive 18F-FDG PET/CT further testify the role of TgAb as surrogate tumor marker in DTC.

Radioiodine therapy of hyperfunctioning thyroid nodules: usefulness of an implemented dose calculation algorithm allowing reduction of radioiodine amount.

AIM: Radioiodine is a common option for treatment of hyperfunctioning thyroid nodules. Due to the expected selective radioiodine uptake by adenoma, relatively high "fixed" activities are often used. Alternatively, the activity is individually calculated upon the prescription of a fixed value of target absorbed dose. We evaluated the use of an algorithm for personalized radioiodine activity calculation, which allows as a rule the administration of lower radioiodine activities. METHODS: Seventy-five patients with single hyperfunctioning thyroid nodule eligible for 131I treatment were studied. The activities of 131I to be administered were estimated by the method described by Traino et al. and developed for Graves'disease, assuming selective and homogeneous 131I uptake by adenoma. The method takes into account 131I uptake and its effective half-life, target (adenoma) volume and its expected volume reduction during treatment. A comparison with the activities calculated by other dosimetric protocols, and the "fixed" activity method was performed. 131I uptake was measured by external counting, thyroid nodule volume by ultrasonography, thyroid hormones and TSH by ELISA. RESULTS: Remission of hyperthyroidism was observed in all but one patient; volume reduction of adenoma was closely similar to that assumed by our model. Effective half-life was highly variable in different patients, and critically affected dose calculation. The administered activities were clearly lower with respect to "fixed" activities and other protocols' prescription. CONCLUSION: The proposed algorithm proved to be effective also for single hyperfunctioning thyroid nodule treatment and allowed a significant reduction of administered 131I activities, without loss of clinical efficacy.

A study of the efficacy of radioiodine therapy with individualized dosimetry in Graves' disease: need to retarget the radiation committed dose to the thyroid.

Although Iodine-131 (131I) therapy is fully validated for Graves' disease (GD), there is debate about radioiodine amount to be administered (prescribed activity), as well as the use of individualized dosimetry vs fixed 131I activity. The clinical outcome of 119 GD patients treated with 131I from 2003 to 2008 has been evaluated. The prescribed activity was calculated according to a dosimetric protocol taking into account several variables, including thyroid volume reduction during treatment. In addition, we performed a simulation according to other dosimetric protocols, by calculating the corresponding prescribed activities. The patients were followed up for at least 12 months after treatment. In the first period of observation (2003), a 120-200 Gray (Gy) radiation dose to the thyroid was prescribed, according to the guidelines published by the Italian Societies of Endocrinology, Nuclear Medicine and Medical Physics: hyperthyroidism cure with a single radioiodine administration was obtained in 53% of patients. This outcome raised up to 89% when a higher radiation dose to the target (200- 250 Gy) was prescribed, although the administered activities were still lower, as a rule, than the most commonly employed fixed activities (400-600 Mega-Becquerel--MBq). Our method showed a high level of individual dose optimisation, particularly when compared to simplified methods. In conclusion, the protocol adopted in this study ensures a satisfactory rate of hyperthyroidism cure, while administering quite low 131I activities, provided that an adequate committed radiation dose to the thyroid is prescribed. In this context, the dose indication given by the aforementioned guidelines should probably be revised.