title: Re-ablation I-131 activity does not predict treatment success in low- and intermediate-risk patients with differentiated thyroid carcinoma.
abstract: The aim of this study was to evaluate the efficacy of different radioactive iodine (I-131) activities used for re-ablation, to compare various combinations of treatment activities, and to identify predictors of re-ablation failure in low- and intermediate-risk differentiated thyroid carcinoma (DTC) patients. The study included 128 consecutive low- and intermediate-risk patients with DTC with ablation failure after total thyroidectomy. Patient characteristics, T status, tumor size, lymph node involvement, postoperative remnant size on whole-body scintigraphy, serum thyroglobulin (Tg), thyroid-stimulating hormone (TSH), anti-Tg antibody (TgAb), and Tg/TSH ratio were analyzed as potential predictors of the re-ablation success. Re-ablation was successful in 113 out of 128 patients (88.3 %). Mean first I-131 activity was 2868 ± 914 MBq (77.5 ± 24.7 mCi) and mean second I-131 activity 3004 ± 699 MBq (81.2 ± 18.9 mCi). There was no association between the first, second, and cumulative activity with re-ablation treatment outcome. Treatment failure was associated with higher Tg levels prior to re-ablation (Tg2) (OR 1.16, 95 % CI 1.05-1.29, P = 0.003) and N1a status (OR 3.89, 95 % CI 1.13-13.41, P = 0.032). After excluding patients with positive-to-negative TgAb conversion, Tg2 level of 3.7 ng/mL predicted treatment failure with a sensitivity of 75.0 %, specificity of 80.5 %, and a negative predictive value of 97.1 %. Patients with positive-to-negative TgAb conversion had higher failure rates (OR 2.96, 95 % CI 0.94-9.29). Re-ablation success was high in all subgroups of patients and I-131 activity did not influence treatment outcome. Tg may serve as a good predictor of re-ablation failure. Patients with positive-to-negative TgAb conversion represent a specific group, in whom Tg level should not be used as a predictive marker of treatment outcome.
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia. marin.prpic@kbcsm.hr.
authors.forename: Marin
authors.initials: M
authors.lastname: Prpic
authors.affiliation: Division of Endocrinology, Diabetes and Metabolic Diseases "Mladen Sekso", Department of Internal medicine, University Hospital Center "Sestre Milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Kruljac
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Davor
authors.initials: D
authors.lastname: Kust
authors.affiliation: Division of Endocrinology, Diabetes and Metabolic Diseases "Mladen Sekso", Department of Internal medicine, University Hospital Center "Sestre Milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Lora S
authors.initials: LS
authors.lastname: Kirigin
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Tomislav
authors.initials: T
authors.lastname: Jukic
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Nina
authors.initials: N
authors.lastname: Dabelic
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Ante
authors.initials: A
authors.lastname: Bolanca
authors.affiliation: Department of Oncology and Nuclear Medicine, University Hospital Center "Sestre milosrdnice", Vinogradska cesta 29, 10000, Zagreb, Croatia.
authors.forename: Zvonko
authors.initials: Z
authors.lastname: Kusic
mesh_terms: D000230:Adenocarcinoma / Q000175:diagnosis* / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D000328:Adult; D001323:Autoantibodies / Q000097:blood; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D013954:Thyroglobulin / Q000097:blood; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery; D013965:Thyroidectomy; D016896:Treatment Outcome
chemical_list: D001323:Autoantibodies; D007457:Iodine Radioisotopes; C006606:anti-thyroglobulin; D013954:Thyroglobulin
keywords: Anti-Tg antibody; Radioactive iodine; Radioiodine ablation; Thyroglobulin