The value of somatostatin receptor imaging with In-111 Octreotide and/or Ga-68 DOTATATE in localizing Ectopic ACTH producing tumors

Abstract

Objective: We aimed to evaluate the value of somatostatin receptor imaging (SRI) with In-111 octreotide and Ga-68 DOTATATE in localizing ectopic ACTH producing tumors.

Methods: Nineteen patients who had In-111 octreotide somatostatin receptor scintigraphy (SRS) and/or Ga-68 DOTATATE PET-CT to localize ectopic ACTH producing tumors between the years 2000 and 2012 were included retrospectively in our study. The results of SRI were compared with clinical onset, radiological findings and surgical data of the patients.

Results: Sixteen In-111 octreotide SRS and five Ga-68 DOTATATE PET-CT were performed in 19 patients. In eight out of 19 patients, ectopic ACTH secretion site could be detected. In five patients, SRS showed pathologic uptake. In four of these patients, surgery revealed pulmonary carcinoid tumors and in one patient pancreatic neuroendocrine tumor. In one patient, Ga-68 DOTATATE PET-CT revealed pathologic uptake in lung nodule which came out to be pulmonary carcinoid tumor. In another patient who had resection of metastases of atypical carcinoid tumor prior to scans, new metastatic foci were detected both with SRS and Ga-68 DOTATATE PET-CT imaging. In one patient, although SRS was negative, CT which was performed three years later showed a lung nodule diagnosed as pulmonary carcinoid tumor. In 11 patients, ectopic ACTH secretion site could not be detected. In 10 of those patients, scintigraphic and radiological imaging did not show any lesions and in one patient, Ga-68 DOTATATE PET-CT was false positive.

Conclusion: SRI has a complementary role with radiological imaging in localizing ectopic ACTH secretion sites. PET-CT imaging with Ga-68 peptide conjugates is a promising new modality for this indication.

Conflict of interest: None declared.

Keywords: Cushing syndrome; ectopic ACTH Syndrome; gallium radioisotopes; indium-111-octreotide; positron-emission tomography/computed tomography; scintigraphy; somatostatin receptor.

Figure 1. Summary of patient outcomesSRI: Somatostatin receptor imagingPt: patient

Figure 2. Planar images of In-111 octreotide SRS of 4 patients are shown: Pulmonary carcinoid tumors (A-C) and pancreatic neuroendocrine tumor (D) Please provide a better copy of Figure 2 C).

Figure 3. Planar and SPECT images of In-111 octreotide SRS of a patient with pulmonary carcinoid tumor. Although the planar image is negative (A), in sagittal (B), coronal (C) and axial (D) SPECT images the lesion can be seen

Figure 4. The centrally located pulmonary nodule in right lung lower lobe cannot be detected easily in CT image, but there is high Ga-68 DOTATATE uptake in PET image. The nodule can be easily detected in PET-CT fusion image.

Figure 5. The moderate Ga-68 DOTATATE uptake in the left adrenal lesion led to false positive interpretation of the image as the site of ectopic ACTH secretion, but the pathology revealed adrenal adenoma without ACTH staining.