Comparative detection rates and potential clinical management implications of 18F-FDG PET/CT and 68Ga-DOTATOC PET/CT in differentiated thyroid carcinoma patients with thyroglobulin-elevated negative iodine scintigraphy: a prospective exploratory study

To explore the detection rates, concordance patterns, and potential clinical management implications of 18 F-FDG PET/CT and 68 Ga-DOTATOC PET/CT in patients with differentiated thyroid carcinoma (DTC) presenting with thyroglobulin-elevated negative iodine scintigraphy (TENIS) syndrome. This prospective single-center exploratory study included 20 patients with histologically confirmed DTC who had elevated serum thyroglobulin (Tg) levels and negative diagnostic or post-therapy radioiodine whole-body scans. All patients underwent both 18 F-FDG PET/CT and 68 Ga-DOTATOC PET/CT. Concordance and discordance between imaging modalities, lesion distribution, SUVmax values, and potential treatment implications were assessed. Nineteen patients had papillary thyroid carcinoma, and one had follicular thyroid carcinoma. Positive findings were observed in 14/20 patients (70%) on 18 F-FDG PET/CT and in 13/20 patients (65%) on 68 Ga-DOTATOC PET/CT. Across all patients, 27 lesions were identified by at least one imaging modality; both modalities demonstrated uptake in 23 lesions. Four lesions showed discordant uptake patterns between the two tracers. McNemar’s test showed no significant difference between the overall positivity rates of the two modalities ( p > 0.999). A statistically significant difference was identified between 18 F-FDG-positive patients and those with negative findings ( p = 0.015). 18 F-FDG PET/CT and 68 Ga-DOTATOC PET/CT demonstrated comparable overall detection rates, with partially overlapping but occasionally discordant lesion distribution patterns. The identification of somatostatin receptor-positive lesions on 68 Ga-DOTATOC PET/CT could potentially have implications for treatment selection, particularly PRRT eligibility. Not applicable.