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.