A gamma detector probe with ex vivo detection of carcinoid tumors superior to intraoperative palpation.

Abstract

Despite the generally successful scintigraphic detection of endocrine tumors with [(111)In]-DTPA-D-[Phe1]-octreotide (OctreoScan, Mallinckrodt Medical, Petten, The Netherlands), its intraoperative application awaits the development of suitable gamma detectors. This study describes a novel probe (H-probe2) and its ex vivo efficacy for the detection of midgut carcinoid tumors. The probe measures 180 mm x 24 mm, and contains a bismuth germinate crystal connected to a photomultiplicator tube, a lead shield, and a tantalum collimator with an angled, 3-mm wide opening. It was characterized in a test bench utilizing solublilized (111)In and 99mTc, and 8 fresh operative specimens containing 26 histologically verified midgut carcinoid tumors (2-40 mm) from patients exposed to OctreoScan. Measurements were made at 2.5-mm intervals over the entire specimens and presented three dimensionally. The test bench analysis supported efficient shielding, and a total collimation of 27 degrees for (111)In and 20 degrees for 99mTc. In addition to 18 palpable tumors, 4 of 6 surgically occult tumors (2-3 mm in dimension) could be discovered with H-probe2. Small 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 surrounding normal tissue. Ex vivo analysis of H-probe2 supported detection of tumors inaccessible to surgical palpation, but its clinical efficiency awaits intraoperative evaluation.