[en] Full text: Aim: To evaluate the role of ⁶⁸Ga-DOTANOC PET/CT in whole body radioiodine scan negative recurrent differentiated thyroid cancer and comparison with ¹⁸F-FDG PET/CT. Materials and Methods: In this prospective study 32 patients of differentiated thyroid cancer presenting with increased Tg value and having no abnormal concentration on whole body radioiodine scan were included. Patients underwent both ⁶⁸Ga-DOTANOC PET/CT and ¹⁸F-FDG PET/CT in random order within 4 weeks time interval. Patient showing lesion(s) on either of scan was considered as recurrent disease positive and substantiated by structural imaging. Tumor lesions were categorised according to four sites-local, nodal, pulmonary and skeletal for comparison of detection rate between two functional modalities. Total number of lesions was defined as sum of number of lesions detected by at least one of the two scans. The analysis is performed on the basis of patient data, and as well as lesion wise. Results: Positive recurrent disease was observed in 24/32 (75%) on either of the scans. In 13/32 (40%) of these patients both imaging modalities detected metastatic disease. In 8/32 (26%) patients disease was detected only by ¹⁸F-FDG PET/CT and in 3/32 (9%) patients only ⁶⁸Ga-DOTANOC PET/CT diagnosed disease. ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTANOC PET/CT showed moderate agreement (k=0.313, P-value=0.03) in detecting disease on patient basis which is statistically significant. Total number of positive lesions detected on either of the modality was 73. ¹⁸F-FDG PET/CT showed 64/73 (87%) lesions and ⁶⁸Ga-DOTANOC PET/CT detected 31/73 (42%) lesions. ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTANOC PET/CT showed 22/73 (30%) concordant lesions. Lesions detected only by ¹⁸F-FDG PET/CT were 33/73 (45%) and only by ⁶⁸Ga-DOTANOC PET/CT 9/73 (12%). Location-wise tumor lesion detection showed fair agreement between two modalities for local (k=0.720) and skeletal (k=0.6) disease. However, detection for nodal (k=0.32) and pulmonary (k=0.24) sites showed moderate agreement only. Conclusion: Disease detection rate is comparable by ¹⁸F-FDG PET/CT and ⁶⁸Ga-DOTANOC PET/CT. Though number of lesions detected by ¹⁸F-FDG PET/CT exceeds far more than ⁶⁸Ga-DOTANOC PET/CT yet somatostatin receptor based scintigraphy provides one additional tool for diagnosing recurrent disease and provides an option for evaluation of patient for peptide receptor radionuclide therapy. In fact, we have already treated few patients with PRRT