Dual-time point PET evaluation of pulmonary malignancy: Determining the likelihood of malignancy

Abstract

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Objectives: We evaluate an efficacy of dual-time point PET imaging in assessing the malignancy in the patients presenting with pulmonary nodule or opacity without and with prior radiation therapy in the lung.

Methods: We evaluated 92 FDG PET scans retrospectively in the two group of patients presenting with new pulmonary mass/nodule/opacity without prior history of lung cancer and treatment(group A: n =38) and new pulmonary nodule/opacity in the patients with prior lung cancer and radiotherapy (Group B: n=54). PET scan was done either with PET or PET/CT without IV contrast. PET Imaging was performed by utilizing a dual-time point imaging at one hour after the injection (IU: initial uptake phase) and 2 hour after injection (DU: delayed uptake phase).

Results: In group A patients, using a conventional criterion of SUV 2.5 on IU yielded sensitivity and specificity of 85% and 72%. SUV criterion of greater 3 on DU (based ROC cut-off) showed sensitivity and specificity of 85% and 83%. In group B, by using SUV of 2.5, sensitivity and specificity shows 86% and 75%; SUV of 3.0 on DU yielded sensitivity, specificity of 87%, and 76%. In group B, there is no statistical significance between the initial and delayed PET imaging in the sensitivity, and specificity. Most of false-positives are noted in the group B patients with CT showing acute radiation changes and inflammation.

Conclusions: Dual-time point PET imaging does improve specificity in the Group A and does not improve in the Group B. Persistent increased FDG uptake had been noted in this group B to 6 months post radiation, during the stage of acute radiation pneumonitis. A false-positive PET scan is high in the patients with prior radiation therapy to the lung. Diagnostic caution is required to determine malignancy and benign in this population of the group.