Vertebral metastases from neuroendocrine tumours: How to avoid false positives on ⁶⁸Ga-DOTA-TOC PET using CT pattern analysis?

Abstract

To develop criteria to improve discrimination between vertebral metastases from neuroendocrine tumours (NETs) and benign bone lesions on PET combined with CT using DOTA-D-Phe¹-Tyr³-octreotide labelled with gallium-68 (⁶⁸Ga-DOTA-TOC). In 535 NET patients, ⁶⁸Ga-DOTA-TOC PET/CT examinations were reviewed retrospectively for vertebral CT lesions and/or PET foci. For each vertebral PET abnormality, appearance on CT, biological volume (BV), standardized uptake value (SUV_max) and ratios to those of reference organs were determined. All vertebral abnormalities were characterized as a metastasis, a typical vertebral haemangioma (VH) or other benign lesion. In 79 patients (14.8 %), we found 107 metastases, 34 VHs and 31 other benign lesions in the spine. The optimal cut-off values to differentiate metastases from benign lesions were BV ≥0.72 cm³, SUVmax ≥2, SUVmax ratio to a reference vertebra ≥2.1, to liver ≥0.28 and to spleen ≥0.14. They corresponded to lesion-based ⁶⁸Ga-DOTA-TOC PET/CT sensitivity of 87 %, 98 %, 97 %, 99 % and 94 %, and specificity of 55 %, 100 %, 90 %, 97 %, 100 %, respectively. The high sensitivity of ⁶⁸Ga-DOTA-TOC-PET/CT in detecting NET vertebral metastases was confirmed; this study showed that specificity could be improved by combining CT features and quantifying ⁶⁸Ga-DOTA-TOC uptake. • Bone metastases in neuroendocrine tumours correlate with prognosis. • Benign bone lesions may mimic metastases on ⁶⁸ Ga-DOTA-TOC PET/CT imaging. • The specific polka-dot CT pattern may be missing in some vertebral haemangiomas. • Lesion atypical for haemangiomas can be better characterized by quantifying ⁶⁸ Ga-DOTA-TOC uptake.