68Ga-DOTATOC PET/CT in Patients with Iodine- and 18F-FDG-Negative Differentiated Thyroid Carcinoma and Elevated Serum Thyroglobulin

Abstract

This study evaluated the impact of ⁶⁸Ga-DOTATOC PET/CT in detecting recurrence or metastases in differentiated thyroid carcinoma (DTC) patients with elevated serum thyroglobulin and both negative radioiodine imaging and negative ¹⁸F-FDG PET/CT.

Methods: ⁶⁸Ga-DOTATOC PET/CT (CT without contrast, low-dose) was performed on average 6 wk after negative ¹⁸F-FDG PET/CT (CT contrast-enhanced, full-dose) in 15 consecutive radioiodine-negative DTC patients with elevated and rising thyroglobulin. Visual assessment of ⁶⁸Ga-DOTATOC PET/CT images used a 4-point scale for classification of lesions (0, no pathologic findings; 1, benign; 2, equivocal; 3, malignant). PET findings were correlated with the histologic subtype of tumor, levels of serum thyroglobulin, and morphologic findings on full-dose CT and neck ultrasound. Histology or clinical and imaging follow-up served as a reference standard. Analysis was performed on a patient and lesion basis.

Results: ⁶⁸Ga-DOTATOC PET/CT was true-positive in 5 patients (10 tumor lesions) and was false-positive in 1 patient. The rate of positive ⁶⁸Ga-DOTATOC PET/CT was significantly higher in poorly differentiated/oxyphilic carcinomas (4/4 patients) than in papillary (1/5) or follicular (0/6) tumors. Thyroglobulin levels tended to be higher in patients with tumor localization on ⁶⁸Ga-DOTATOC PET/CT, but differences were not significant. In 2 of 5 patients with true-positive findings on ⁶⁸Ga-DOTATOC PET/CT, CT alone but not ultrasound identified 2 of 10 tumor lesions, but in both patients ⁶⁸Ga-DOTATOC-PET/CT revealed further tumor lesions not detected on CT alone.

Conclusion: ⁶⁸Ga-DOTATOC PET/CT should be considered in the case of negative ¹⁸F-FDG PET/CT in radioiodine-negative DTC patients with elevated and rising thyroglobulin. Imaging with ⁶⁸Ga-DOTATOC appears promising especially in poorly differentiated and oxyphilic subtypes of DTC.

Keywords: DOTATOC PET/CT; SSTR; differentiated thyroid carcinoma; elevated thyroglobulin; recurrence.