Intraoperative detection of pheochromocytoma with iodine-125 labelled meta-iodobenzylguanidine: a feasibility study

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Abstract
We evaluated the feasibility of intraoperative detection of pheochromocytoma sites after injection of meta-iodobenzylguanidine labelled with iodine-125. Six patients with multiple or recurrent pheochromocytoma were injected for intraoperative detection. During surgery, all count rates were recorded using a CdTe detector diode. Tumour foci were found in all cases. Tumour count rates ranged from 50 to 1000 counts per second (mean ≈400). Blood activity, used as a reference level, ranged from 10 to 50 counts per second (mean ≈35). In all patients, the intraoperative probe was helpful to the surgeon and facilitated the discovery of the pathological foci even when they were small (<1 cm). Complete resection under probe control was correlated with postoperative normalization of urinary normetanephrine excretion. The use of a probe designed to detect low-energy gamma-ray radionuclides bound to a highly specific molecule provides an accurate detection tool which is well adapted for ectopic localizations and for small foci.