An Intrapatient Comparison of 99mTc-EDDA/HYNIC-TOC with 111In-DTPA-Octreotide for Diagnosis of Somatostatin Receptor-Expressing Tumors

摘要

The aim of this study was to compare the imaging abilities of the recently developed somatostatin analog, 99mTc-hydrazinonicotinyl-Tyr3-octreotide (99mTc-HYNIC-TOC [99mTc-TOC]), with 111In-diethylenediaminepentaacetic acid-d-Phe1-octreotide (111In-OCT [Octreoscan]) in patients undergoing routine somatostatin receptor (SSTR) scintigraphy. Methods: Forty-one patients (20 men, 21 women; age range, 29a€“75 y; mean age, 56.7 y) with either histologically proven or biologically and clinically suspected endocrine tumors were enrolled in the study. Four groups were distinguished: (a) patients being evaluated for the detection and localization of neuroendocrine tumors (n = 6), (b) tumor staging (n = 19), (c) patients being investigated to determine the SSTR status of tumor lesions (n = 11), and (d) patient follow-up studies (n = 5). Each patient received a mean activity of 150 MBq 111In-OCT and 350a€“400 MBq 99mTc-TOC. Scintigraphy with 99mTc-TOC was performed 4 h after injection and scintigraphy with 111In-OCT was performed 4 and 24 h after injection. SPECT studies of areas of interest were performed 4 h after injection for both tracers as well as at 24 h after injection for 111In-OCT. The time interval between the studies using each tracer ranged from 2 to 22 d (mean interval, 9.3 d). Results: 111In-OCT and 99mTc-TOC showed an equivalent scan result in 32 patients (78%), 9 cases showed discrepancies (22%), false-negative results with 111In-OCT were seen in 6 cases (14.6%), whereas 99mTc-TOC was false-positive in 2 cases (4.9%). 111In-OCT was true-negative in both cases. The false-positive findings of the 99mTc-TOC studies were caused by nonspecific uptake in the bowel. In 1 case, 99mTc-TOC correctly identified a metastasis in the lumbar spine but both scan results were false-positive because of an inflammatory process. In 21 patients with SSTR-expressing tumors, the semiquantitative region-of-interest analysis showed that 99mTc-TOC achieved higher tumor-to-normal tissue ratios than 111In-OCT. Conclusion: This study revealed a higher sensitivity of 99mTc-TOC as compared with 111In-OCT as an imaging agent for the localization of SSTR-expressing tumors. To avoid false-positive findings with 99mTc-OCT due to nonspecific tracer accumulation, additional scanning at 1a€“2 h after injection should be done.