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Comparative evaluation of 99mTc-depreotide and 201Tl chloride single photon emission tomography in the characterization of pulmonary lesions

PurposeTo compare 99mTc-depreotide and 201Tl chloride SPET in the characterization of pulmonary lesions. MethodsFifty-seven pulmonary lesions from 33 patients suspected of malignancy in computed tomography, were assessed by 99mTc-depreotide and 201Tl early and delayed SPET imaging. Images were visually assessed and the tumour-to-normal (T/N) lung activity ratio for early (ER) and delayed (DR) scans and the retention index (RI), were calculated in every lesion. A final diagnosis was reached for all lesions, based either on histology or prolonged clinical and radiological follow-up. ResultsTwenty-three lesions were characterized as malignant and 34 benign. In visual analysis, all malignant lesions accumulated both tracers resulting in sensitivity and negative predictive values of 100%. However, false positive interpretations resulted in a specificity of 64.7% and 67.6% for 99mTc-depreotide and 201Tl, respectively. ER and DR of both agents and the RI of 99mTc-depreotide were significantly higher in malignant, compared to benign lesions. In defining thresholds of abnormality from ROC analysis, a significant increase in specificity was observed for both tracers in both scan phases (91.2% for all), as compared to visual analysis (P<0.01). There was no significant difference in the diagnostic performance between 99mTc-depreotide DR and 201Tl DR, although the former provided the highest T/N ratio. ConclusionThis study demonstrates that 99mTc-depreotide and 201Tl SPET are equally effective and may be useful in the non-invasive determination of lung malignancy. The specificity of both techniques is significantly improved by quantifying radiopharmaceutical accumulation in pulmonary lesions.