A multicenter 18F-FDG-PET/CT study in solitary pulmonary nodule: Qualitative and Semiquantitative parameters to predict the risk of malignancy

Aim/Introduction: Most of diagnostic accuracy studies with 18F-FDG-PET/CT are limited by the use of a single threshold for distinguishing malignant from benign solitary pulmonary nodules (SPN).The aim of this study is to evaluate the reliability of 18F-FDGPET/CT and correlate qualitative and semiquantitative parameters, analysed either individually or as a whole, in patients with SPN, in order to predict the risk of malignancy. Materials and Methods: 146 patients (49 females, 97 males, mean age 68±8,32 years) positive for SNP at 18F-FDG-PET/CT, according to their pre-test probability of malignancy determined by the presence of risk factors were retrospectively evaluated.Cytopathological examination of samples, considered to be the gold standard for lung cancer diagnosis, was performed in order to assess malignancy of the lesions.Qualitative parameters with 3 points scoring system (high, medium or absent uptake),dimension and site of SPN, as well as semiquantitative parameters(TLG,MTV,SUVmax,SUVmean) were taken in account. Results: Among the 146 patients who underwent FDG-PET/CT subsequent cytopathological examination of specimens was found to be positive in 100(68.4%) cases. Visual analysis revealed that FDG uptake was absent in 20 patients(13,69%), moderate in 44(30,13%) and intense in 82(56.16%) patients. The mean dimension at CT of SPN was 18.28(±8.32) mm, 58 were localized in the inferior lobe, 74 in the superior lobe and 14 in the medium lobe.No statistical signifcance was found between the tracer uptake, the dimension or the site of the SPN and the risk of malignancy. The pre-test probability of malignancy doesn’t correlate signifcantly with any semiquantitative parameters taken in account, but a direct correlation was observed between the diameter of the SPN at CT and the pre-test probability of malignancy. Average values for semiquantitative parameters were found:SUVmax 6.53±4.63, SUVmean 3.508±2.234, TLG 19.88±33.45, MTV 3.29±2.99.Optimal cut-ofs for semiquantitative parameters, in terms of predictive values, have been found: a cut-of of 3.625 of SUVmax has 86.6% sensitivity and 69.1% specifcity; SUVmean’s optimal cut-of is 2.51, with 79.1% sensitivity and 76.3% specifcity; an MTV cut-of of 2.55 shows 74.7% sensitivity and 70.9% specifcity while a TLG’s cut-of of 11.8 shows 66% sensitivity and 83.6% specifcity. Conclusion: This study showed that qualitative and semiquantitative analysis of SPNs at 18F-FDG PET/CT can be very important in assessing the probability of malignancy.TLG has shown to be directly correlated to SUVmax and SUVmean and can be used as a predictive parameter for malignancy.No correlations have been found between the pretest probability of malignancy and the semiquantitative parameters.