Improved tumour detection by gastrin receptor scintigraphy in patients with metastasised medullary thyroid carcinoma

Purpose: Radiopeptide imaging is a valuable imaging method in the management of patients with neuroendocrine tumours (NET). To determine the clinical performance of gastrin receptor scintigraphy (GRS), it was compared with somatostatin receptor scintigraphy (SRS), computed tomography (CT) and F-18-FDG positron emission tomography (PET) in patients with metastasised/recurrent medullary thyroid carcinoma (MTC). Methods: Twenty-seven consecutive patients underwent imaging with GRS, SRS (19 patients), CT and PET (26 patients). GRS and SRS were compared with respect to tumour detection and uptake. CT, PET, magnetic resonance imaging (MRI), ultrasound (US) and follow-up were used for verification of findings. In addition, GRS, CT and PET were directly compared with each other to determine which method performs best. Results: Nineteen patients underwent both GRS and SRS. Among these, GRS showed a tumour detection rate of 94.2% as compared to 40.7% for SRS [mean number of tumour sites (+/- SD) and 95% confidence intervals (CI): GRS 4.3 +/- 3.1/2.8-5.7, SRS 1.8 +/- 1.6/1.1-2.6]. In 26 patients, GRS, CT and PET were compared. Here, GRS showed a tumour detection rate of 87.3% (CT 76.1%, PET 67.2%; mean number of tumour sites and 95% CI: GRS 4.5 +/- 4.0/2.9-6.1, CT 3.9 +/- 3.5/2.5-5.3, PET 3.5 +/- 3.3/2.1-4.8). If GRS and CT were combined, they were able to detect 96.7% of areas of tumour involvement. Conclusion: GRS had a higher tumour detection rate than SRS and PET in our study. GRS in combination with CT was most effective in the detection of metastatic MTC.