Abstract
Aim: In-111 DTPA-octrotide (In-111 DTPAOC) has proven its usefulness in the detection of somatostatin receptor (STTR) expressing NETs and their metastases. One of the major problems of this imaging modality is its limited sensitivity in detecting small lesions, particularly of the skeletal system, even if it is carried out in SPECT-technique. Ga-68 DOTA-D-Phe(1)-Tyr(3)-octreotide (Ga-68 DOTOATOC) is a new PET radiotracer with a higher affinity to STTR2 compared to In-111 DTPAOC. In this study we evaluated the clinical performance of Ga-68 DOTATOC-PET/CT and conventional bone scintigraphy in detecting skeletal metastases of STTR2-positive NETs. Material and Methods: Fourteen patients with metastatic NETs were included in this study recieving both conventional bone scintigraphy with Tc-99m DPD (GE Millennium VG gamma camera) and Ga-68 DOTATOC-PET/CT (GE Discovery LS PET/CT-scanner). Bone scintigraphy was performed two hours post injection of 560 MBq Tc-99m DPD. The PET/CT scan was carried out 20min. p.i. of Ga-68 DOTATOC (80–120 MBq). Osseous lesions shown in both techniques were analysed and compared. Results: Bone scintigraphy revealed osseous lesions in 11 of 14 patients. In two patients the bone scans were equivocal. Ga-68 DOTATOC-PET/CT illustrated skeletal metastases in all patients with high image quality. Disseminated metastases were shown in six patients whereas bone scintigraphy was not able to demonstrate the whole extent of osseous metastatic involvement. In three of these patients Ga-68 DOTATOC-PET/CT was able to show even subtle osseous lesions. In all patients, lesion localisation was significantly more precise with Ga-68 DOTATOC-PET/CT. Conclusion: Compared to conventional bone scintigraphy, integrated PET/CT with Ga-68 DOTATOC significantly improves detection of bone metastases of STTR2-positive tumors. The new ligand Ga-68 DOTATOC itself as well as the greater imaging potential (spatial resolution about 3–4mm) of PET/CT might be responsible for these observations. For clinical practice: If Ga-68 DOTATOC-PET/CT is available, an additional bone scan for detection of skeletal metastases is not necessary.
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