Evaluation of the role of [18F]FDG-PET/CT and [68Ga]DOTATOC-PET/CT in differentiating typical and atypical pulmonary carcinoids

Pulmonary carcinoids are histologically classified into typical and atypical. It is important to identify these preoperatively for treatment planning and prognosis. Structural imaging cannot conclusively differentiate between them. The aim of this study was to assess the possibility of differentiating the 2 variants using [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) and [68Ga]1,4,7,10-tetraazacyclododecane-N(I-IIII)-tetraacetic acid-(D)-Phe1-Thy3-octreotide (DOTATOC)-PET/CT. The imaging results of 20 patients with pulmonary carcinoids (13 typical, 7 atypical) on [18F]FDG-PET/CT and [68Ga]DOTATOC-PET/CT were assessed retrospectively. Six typical carcinoids failed to reveal significant uptake on [18F]FDG-PET/CT. All the atypical carcinoids revealed significant uptake on the [18F]FDG-PET/CT that was higher than that in typical carcinoids (standardized uptake value (SUV)max, 2.9-8.4, P = 0.001). The SUVmax in typical carcinoids on [68Ga]DOTATOC-PET/CT was significantly higher (SUVmax, 8.8-66) compared with atypical carcinoids (SUVmax, 1.1-18.5, P = 0.002). Ratios of SUVmax on [68Ga]DOTATOC-PET/CT to that on [18F]FDG-PET/CT were significantly higher (P < 0.001) in typical carcinoids compared with atypical carcinoids. The different uptake patterns on [18F]FDG and [68Ga]DOTATOC-PET/CT. and the ratio of SUVmax may be helpful in differentiating between typical and atypical carcinoids.