68Ga-DOTATOC PET/CT in the localization of metastatic extra-adrenal paraganglioma and pheochromocytoma compared with 18F-DOPA PET/CT

Abstract

Objective: ¹⁸F-Fluoro-L-dihydroxyphenylalanine (¹⁸F-DOPA) PET offers high sensitivity and specificity in the imaging of non-malignant extra-adrenal paraganglioma (PGL) and pheochromocytoma (PHEO) but lower sensitivity in metastatic disease. These tumours are of neuroendocrine origin and can be detected by ⁶⁸Ga-DOTA-Tyr3-octreotide (⁶⁸Ga-DOTA-TOC) PET. Therefore, we compared ⁶⁸Ga-DOTA-TOC and ¹⁸F-DOPA as radiolabels for PET/CT imaging for the diagnosis of metastatic extra-adrenal PGL and PHEO. Combined cross-sectional imaging was the reference standard.

Methods: A total of 6 men and 4 women (age range 22-72 years) with anatomical and/or histologically proven metastatic PGL and PHEO were included in this study. Of these patients, 2 male patients suffered from PHEO, while the remaining 8 patients were diagnosed as metastatic extra-adrenal PGL disease. Comparative evaluation included morphological imaging with CT and functional imaging with ⁶⁸Ga-DOTA-TOC and ¹⁸F-DOPA PET. The imaging results were analyzed on a per-lesion basis. The maximum standardized uptake value (SUV_max) of each functional imaging modality in concordant tumour lesions was measured.

Results: Compared with anatomical imaging, the per-lesion detection rate of ⁶⁸Ga-DOTA-TOC was 100% (McNemar, P<0.01), and that of ¹⁸F-DOPA PET was 82.3% (McNemar, P<0.8) in metastatic extra-adrenal PGL and PHEO. Overall, ⁶⁸Ga-DOTA-TOC PET identified 67 lesions; anatomical imaging identified 62 lesions, and ¹⁸F-DOPA PET identified 56 lesions. The SUV_max (mean±SD) of all concordant lesions was 29.3±19.9 for ⁶⁸Ga-DOTA-TOC PET and 12.3±9.1 for ¹⁸F-DOPA PET (Mann-Whitney U test, P<0.0001).

Conclusion: ⁶⁸Ga-DOTA-TOC PET offers the highest detection rate in metastatic extra-adrenal PGL and PHEO compared to ¹⁸F-DOPA PET and even to diagnostic CT, particularly in bone lesions. Combined functional/anatomical imaging (⁶⁸Ga-DOTA-TOC PET/CT) enables exact tumour extension to be detected in these rare tumour entities, especially in the case of unclear anatomical correlation.

Keywords: (18)F-DOPA; (68)Ga-DOTA-TOC; Extra-adrenal paraganglioma; Feocromocitoma; PET; Paraganglioma extra-adrenal; Pheochromocytoma.