Value of Peptide Receptor Scintigraphy Using 123I-Vasoactive Intestinal Peptide and 111In-DTPA-D-Phe1-Octreotide in 194 Carcinoid Patients: Vienna University Experience, 1993 to 1998

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Abstract
PURPOSE: To report our experience with both 123I-vasoactive intestinal peptide (VIP) and 111In-DTPA-D-Phe1-octreotide for imaging to identify primary and metastatic tumor sites in carcinoid patients. PATIENTS AND METHODS: One hundred ninety-four patients with a verified or clinically suspected diagnosis of a carcinoid tumor were injected with 111In-DTPA-D-Phe1-OCT for imaging purposes, while 133 patients underwent scanning with both 123I-VIP and 111In-DTPA-D-Phe1-OCT in random order. Imaging results were compared with computed tomography scans, results of conventional ultrasound, endosonography, and endoscopy, and results of surgical exploration in case of inconclusive conventional imaging. RESULTS: Primary or recurrent carcinoid tumors could be visualized with 111In-DTPA-D-Phe1-OCT in 95 (91%) of 104 patients; metastatic sites were identified in 110 (95%) of 116 patients. In 11 (51%) of 21 patients with suggestive symptoms but without identified lesions by conventional imaging, focal tracer uptake located the carcinoid tumor. In addition, metastatic disease was demonstrated in three patients after resection. In a direct comparison in the 133 patients who underwent both imaging modalities, 111In-DTPA-D-Phe1-OCT was found to be superior to 123I-VIP, with 35 (93%) of 38 versus 32 (82%) of 38 scans being positive in primary or recurrent tumors, 58 (90%) of 65 versus 53 (82%) of 65 being positive in patients with metastatic sites, and seven (44%) of 16 versus four (25%) of 16 being positive in patients with symptoms but otherwise negative work-ups. Overall, additional lesions not seen on conventional imaging were imaged in 43 (41%) of 158 versus 25 (25%) of 103 scans with 111In-DTPA-D-Phe1-OCT and 123I-VIP, respectively. CONCLUSION: Both peptide tracers have a high sensitivity for localizing tumor sites in patients with ascertained or suspected carcinoid tumors, with 111In-DTPA-D-Phe1-OCT scintigraphy being more sensitive than 123I-VIP receptor scanning. Both, however, had a higher diagnostic yield than conventional imaging, as verified by surgical intervention or long-term follow-up. The combination of both peptide receptor scans does not seem to further enhance diagnostic information.