Comparative analysis of 99m Tc-depreotide and 99m Tc-EDDA/HYNIC-TOC thorax scintigrams acquired for the purpose of differential diagnosis of solitary pulmonary nodules

Abstract

BACKGROUND: Aiming at comparison of diagnostic efficacy of 2 radiopharmaceuticals: ^99mTc-depreotide (Neospect, Amersham) and ^99mTc-EDDA/HYNIC-Tyr³-octreotide (Tektrotyd, Polatom), in differentiation between malignant and benign etiology of solitary pulmonary nodules (SPNs), radionuclide studies with 2 radiotracers were performed in 18 patients.
MATERIAL AND METHODS: For both radiopharmaceuticals the same acquisition and processing protocols were applied. Studies were acquired with SPECT technique, after administration of 740 MBq of activity. Scintigrams were assessed visually, as: positive (+), equivocal (+/–) and negative (–). Additionally, uptake intensity of both radiotracers in nodules was assessed semiquantitatively, using a tumour-to-background ratio. Verification of scintigraphic results was based in 14 cases upon a pathological examination of tumour samples (histopathology) and in the remaining 4 - on clinical observation and bacteriological studies.
RESULTS: Normal scintigrams obtained with both radiopharmaceuticals differed significantly. ^99mTc-depreotide was markedly accumulated in spine, sternum, ribs and lungs (mean lung/heart ratio = 2.2). This accumulation was not observed on ^99mTc- -EDDA/HYNIC-TOC scintigrams (mean lung/heart ratio = 0.7). In 6 patients a malignant etiology - lung cancer - was revealed (5 - adenocarcinoma, 1 - squamous cell) and the other 12 cases turned out to be benign (4 hamartomas, 3 tuberculomas, a tuberculous infiltrate, an alien body with inflammatory reaction, a hyperplasia of lymphatic tissue and 2 cases of unknown etiology, from which one had a stable size and the other resolved during a 6 month observation period). In all 6 cases of lung cancer positive results were obtained with both tracers. Moreover, in 2 patients metastases in mediastinum could be observed on scintigrams obtained with both radiopharmaceuticals. From among 12 cases of benign etiology 6 ^99mTc-depreotide scintigrams were true negative, 1 - equivocal and 5 - false positive, whereas 6 ^99mTc-EDDA/HYNIC-TOC scintigrams were true negative, 4 - equivocal and 2 false positive. Moreover, ^99mTc-depreotide additionally revealed mediastinal and hilar lesions in 9 patients with benign lesions and ^99mTc-EDDA/HYNIC-TOC - in 8. A visual comparison of scintigrams revealed a higher quality of ^99mTc-Depreotide images in comparison with ^99mTc-EDDA/HYNIC-TOC ones. ^99mTc-Depreotide showed a higher than ^99mTc-EDDA/HYNIC-TOC accumulation in lung tumours compared with blood pool (heart) - 4.5 (s.d. 1.05) and 1.8 (s.d. 0.29), respectively (p < 0.05). However, mean values of tumour-to-lung-background ratio were equal for both radiotracers (2.2 in malignant and 1.4 in benign lesions, respectively). A statistically significantly higher non-uniformity of counts inside lung background regions was found on ^99mTc-EDDA/HYNIC-TOC scintigrams than on ^99mTc-depreotide ones (16.4% vs. 11.4%; p < 0.01).
CONCLUSIONS: Although both radiopharmaceuticals show similar diagnostic efficacy in differentiation of SPNs, a tendency toward a higher number of false positive results on ^99mTc-depreotide scintigrams probably leads to a lower specificity. Better statistical quality of ^99mTc-depreotide scintigrams facilitates their interpretation and a distinct outline of lungs simplify localization of lesions. A substantial number of false positive lesions in mediastinal and hilar regions in patients without a neoplastic process hamper the usefulness of both radiotracers for effective detection of lung cancer metastases to lymph nodes.