Aim: To evaluate the use of 99mTc-EDDA-hydrazinonicotinyl-Tyr3-octreotide (Tc-TOC) for staging and follow-up of neuroendocrine gastro-entero-pancreatic (GEP) tumors with special focus on the acquisition protocol including single photon emission computed tomography (SPECT).
Methods: Eighty-eight patients (37 female, 51 male; age range: 16 to 81 years; mean age: 56.3 years) were studied: 42 patients for staging after initial histological confirmation and 46 patients during post-therapy follow-up. An average activity of 400 MBq of the radiopharmaceutical was injected. All tumors originated from neuroendocrine tissue of the gastroenteropancreatic tract. Whole body scintigrams at 4 h postinjection and SPECT of the abdomen were obtained in all patients. Additional planar images of the abdomen were acquired at 2 h after injection in 68 patients.
Results: The Tc-TOC scan result was true-positive in 56 patients, true-negative in 17, false-negative in 14, and false-positive in 1 patient. The false-positive finding was caused by a colonic adenoma. Overall, a scan sensitivity of 80% (56/70 patients), specificity of 94.4% (17/18 patients) and accuracy of 82.9% (73/88 patients) were calculated on patient basis. In total, Tc-TOC detected 357 foci in 69 patients. In 7 patients equivocal findings were observed in the bowel at 4 h postinjection without corresponding tracer uptake in the scan 2 h earlier, meaning that these abnormal findings were correctly classified as non-malignant. In addition to planar views, SPECT revealed further 62 lesions.
Conclusions: Tc-TOC with one-day, dual-time acquisition protocol is an accurate staging procedure in patients with neuroendocrine GEP tumors. SPECT shows high sensitivity for detection of abdominal lesions, while earlier images improve the reliability of abnormal abdominal findings.