Intraoperative gamma probe detection of neuroendocrine tumors

Previous studies of the intraoperative use of a handheld gamma probe to localize metastases and primary tumors of colorectal cancer have shown improved assessment of tumor spread and changes in surgical management based on added information gained by radioimmunoguided surgery. We conducted a prospective study to determine whether intraoperative radiodetection is able to reveal microscopic and occult disease of neuroendocrine tumors [medullary thyroid carcinomas (MTCs), gastroenteropancreatic (GEP) tumors].

After the injection of 180 MBq [111In-diethylenetriaminepentaacetic acid (DTPA)-D-Phe1]pentetreotide and/or 500 MBq 99mTc-dimercaptosuccinic acid (DMSA) (both for double-nuclide scintigraphy), preoperative somatostatin receptor imaging (12 patients with GEP tumors) and double-nuclide scintigraphy (10 patients with relapsing MTCs were performed. The results were combined with the information obtained from conventional imaging modalities (CT and sonography). Intraoperative radiodetection was performed 24 hr after administration of [111In-DTPA-D-Phe1]pentetreotide or 4 hr after the injection of 99mTc-DMSA using a handheld gamma probe.

Intraoperative gamma counting localized 70 somatostatin receptor-positive lesions of GEP tumors, whereas preoperative receptor imaging visualized 74%, surgical palpation visualized 44% and radiological imaging modalities localized only 43%. In 10 patients with recurrent MTCs, the surgeon was successful in localizing and removing 30 tumor lesions using the gamma probe. Twenty-seven of 30 lesions demonstrated tumor involvement, whereas 3 lesions were false-positive (lymphadenitis). Double-nuclide scintigraphy revealed 67% (Octreoscan, 7 of 20; 99mTc-DMSA, 13 of 20), surgical palpation revealed 60% and conventional imaging methods (CT, sonography) revealed only 50% of all lesions detected intraoperatively by the handheld gamma probe. The smallest lesion identified by the handheld probe (not palpated by the surgeon) was a lymph node metastasis (5-mm diameter).

The preliminary data show that intraoperative handheld gamma probe detection of microscopic and occult endocrine tumors is feasible and more sensitive than external scintigraphy and conventional imaging.