Dual time point FDG-PET-CT imaging in differentiating benign from malignant lung nodules: Our experience in 119 patients

Abstract

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Objectives: To assay the usefulness of dual time (1 and 2 hours) 18F-FDG-PET-CT acquisition imaging, in evaluating newly diagnosed lung lesions incidentally discovered and compare with the standard technique.

Methods: In 119 patients (of whom 23 with multiple nodules; 85 m, 34 f; m.a. 67 y), we calculated early and delayed SUV. Final diagnosis was based on histology for patients with a positive PET-CT, while in case of a negative scan, we assumed this correspond to a benign disease if serial CT studies had not demonstrated any progression and patients were free of malignancies at 12 months follow-up.

Results: 54 patients had malignant tumours and 65, benign diseases. Tumour max-SUVs were 7.9 ± 4.7 and 10.4 ± 5.8 at 1 and 2 h respectively, with a mean increase rate of 34.8% ± 26.9% (p < 0.001). Benign lesions had max-SUVs of 1.8 ± 1.3 and 1.8 ± 1.9, with not significant decrease over time (-4.2% ± 20.5%). An early maxSUV threshold of 2.5 accurately differentiated malignancies from benign diseases (sens 91% and spec 83%). Dual time acquisition allows better lesion characterization and evaluating the differential gradient increase, improves accuracy. Even better results are yielded if different cut off values are chosen in case of lesions with early high or low uptake: when early SUV>2.5, a further increase as low as 10% is highly predictive of malignancy, but in low gradient lesions (SUV<2.5), the increase must be higher than 40% to be significant. In this way we got sensitivity and specificity of 96% and 92% respectively. This allowed to correctly identify 6 patients with chronic inflammations, who although had a relatively high early SUV, did not show a further increase at the 2nd hour and three low grade malignant nodules (1 well-differentiated adenocarcinoma, 1 well-differentiated squamous carcinoma, 1 lymphoma), which had an early low SUV, but a > 40% SUV increase by the 2nd hour. We had 2 FN (1 carcinoid and 1 well differentiated adenocarcinoma)and 5 FP (active inflammations or metaplasia).

Conclusions: preliminary data show dual time point imaging FDG-PET-CT with thresholds increase of 10% or 40% if 1h-SUV is higher or lower than 2.5 respectively, improves accuracy (especially for a significant increase of specificity; p< 0.05), in the differential diagnosis of lung lesions.