A GAMMA-DETECTOR PROBE WITH EX-VIVO DETECTION OF CARCINOID-TUMORS SUPERIOR TO INTRAOPERATIVE PALPATION

BACKGROUND. Despite the generally successful scintigraphic detection o f endocrine tumors with [In-111]-DTPA-D-[Phe(1)]-octreotide (OctreoSca n(R), Mallinckrodt Medical, Petten, The Netherlands), its intraoperati ve application awaits the development of suitable gamma detectors. Thi s study describes a novel probe (H-probe2) and its ex vivo efficacy fo r the detection of midgut carcinoid tumors. METHODS. The probe measure s 180 mm x 24 mm, and contains a bismuth germinate crystal connected t o a photomultiplicator tube, a lead shield, and a tantalum collimator with an angled, 3-mm wide opening. It was characterized in a test benc h utilizing solublilized In-111 and Tc-99m, and 8 fresh operative spec imens containing 26 histologically verified midgut carcinoid tumors (2 -40 mm) from patients exposed to OctreoScan(R). Measurements were made at 2.5-mm intervals over the entire specimens and presented three dim ensionally. RESULTS. The test bench analysis supported efficient shiel ding, and a total collimation of 27 degrees for In-111 and 20 degrees for Tc-99m. In addition to 18 palpable tumors, 4 of 6 surgically occul t tumors (2-3 mm in dimension) could be discovered with H-probe2. Smal l tumors in close apposition to a large tumor could not be separated. Wellcounter examination showed that tumors detected with the H-probe2 exhibited 1.7-84.1 times higher radionuclide uptake than the surroundi ng normal tissue. CONCLUSION. Ex vivo analysis of H-probe2 supported d etection of tumors inaccessible to surgical palpation, but its clinica l efficiency awaits intraoperative evaluation. (C) 1997 American Cance r Society.