Preoperative characterization of indeterminate large adrenal masses with dual tracer PET-CT using fluorine-18 fluorodeoxyglucose and gallium-68-DOTANOC: initial results.

PURPOSE: We aimed to evaluate the usefulness of dual tracer positron emission tomography-computed tomography (PET-CT) with flourine-18 fluorodeoxyglucose (18F-FDG) and gallium-68 [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid]-1-NaI3-octreotide (68Ga-DOTANOC) in preoperative characterization of large indeterminate adrenal masses.

MATERIALS AND METHODS: Ten patients (four males, six females; median age, 35 years) with indeterminate, large (≥4 cm) adrenal masses were included in this prospective study. All patients underwent both 18F-FDG PET-CT and 68Ga-DOTANOC PET-CT within one week. Images were evaluated both visually and semi-quantitatively, with standardized uptake value (SUVmax) and SUVratio (SUVmax) of tumor/SUVmax) of mediastinum). Based on differential uptake pattern on 18F-FDG and 68Ga-DOTANOC, lesions were classified as cortical (18F-FDG>68Ga-DOTANOC), medullary (68Ga-DOTANOC>18F-FDG), or indeterminate (18F-FDG=68Ga-DOTANOC). Histopathology was taken as reference standard. Receiver operating characteristic (ROC) analysis was performed to find a cut-off of SUVmax) and SUVratio to differentiate cortical and medullary lesions.

RESULTS: On histopathology, eight lesions were adrenocortical carcinomas, one was benign pheochromocytoma, and one was malignant pheochromocytoma. Visually, 18F-FDG PET-CT was positive in all ten lesions, while 68Ga-DOTANOC PET-CT was positive in two, both of which were pheochromocytomas. On SUVmax) based analysis, nine lesions were cortical and one was medullary. On ROC analysis, a SUVmax) cut-off of > 2.3 was obtained for 18F-FDG PET-CT and 3.6 for 68Ga-DOTANOC PET-CT for differentiating adrenal cortical and medullary lesions. The cut-off for SUVratio was 4.5 on 18F-FDG PET-CT and 11.1 on 68Ga-DOTANOC PET-CT.

CONCLUSION: These preliminary results demonstrate that dual tracer PET-CT using 18F-FDG and 68Ga-DOTANOC could be informative in the preoperative characterization of large indeterminate adrenal masses.