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

OBJECTIVE

F-Fluoro-L-dihydroxyphenylalanine (F-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 Ga-DOTA-Tyr3-octreotide (Ga-DOTA-TOC) PET. Therefore, we compared Ga-DOTA-TOC and F-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 Ga-DOTA-TOC and F-DOPA PET. The imaging results were analyzed on a per-lesion basis. The maximum standardized uptake value (SUV) of each functional imaging modality in concordant tumour lesions was measured.

RESULTS

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

CONCLUSION

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