Localization of Ectopic ACTH Secreting Lesion with Ga-68 DOTANOC PET/CT

442 Introduction: Ectopic ACTH (Adrenocorticotropic Hormone) secretion by non-pituitary tumor contributes to 5-10% of all ACTH dependent hypercortisolism. Most common source of ectopic ACTH secretion is attributed to neuro-endocrine tumors, largely carcinoid tumors of the lung. Cause of endogenous hypercortisolism due to ectopic ACTH secretion can be differentiated from pituitary causes by inferior petrosal sinus sampling (IPSS) for ACTH levels; the difficulty lies in identifying the source of ectopic ACTH secretion. This study aimed at assessing the detection of source of ectopic ACTH syndrome (EAS) using stomatostatin receptor imaging with 68Ga DOTANOC PET/CT. Materials and Methods: All consecutive patients with clinical evaluation suggestive of EAS, referred to our department for 68Ga DOTANOC PET/CT from February 2014 to November 2018, were selected retrospectively. All patients were injected 3-4mCi 68Ga DOTANOC intravenously and underwent whole body PET/CT 30-40 minutes post-injection, on either Biograph mCT PET/CT, Siemens or Discovery 710 PET/CT, GE. Scanned images were interpreted by two nuclear physicans independently. 68Ga DOTANOC PET/CT findings were corroborated with clinical details. Results: Total of 26 patients (18 female, 8 male) with suspected EAS were included in this study. Mean age of patients was 33.61 (±1.94) years. In ten out of twenty-six (38.4%) cases a source for ectopic ACTH secretion could be localized on 68Ga DOTANOC PET/CT. Of these ten, five (50%) were detected in the lungs and one was localized in the duodenum. Two were found to be metastatic disease with skeletal and hepatic involvement. In one case a paraganglioma was detected and in another a supra-renal lesion with increased uptake was noted. Two patients with positive lesions (one in lung and other in duodenum) were previously treated cases of EAS, referred to look for recurrence in view of rising ACTH. Conclusions: 68Ga DOTANOC PET/CT was able to localize the source of ectopic ACTH secretion in 38.4% of cases. This study also suggests the possible role of 68Ga DOTANOC PET/CT in detection of residual or recurrent disease on follow-up of known cases of EAS.