Qualitative and semiquantitative parameters in solitary pulmonary nodule: a multicenter 18F-FDG-PET/CT study

Background-Aim: The aim of this study is to evaluate the reliability
of 18F-FDG-PET/CT qualitative and semiquantitative parameters,
analysed either individually or as a whole, in patients with solitary
pulmonary nodule (SPN), in order to predict the risk of malignancy.
Methods: A retrospective evaluation of 18F-FDG-PET/CT of 146
patients (49 females, 97 males with a mean age of 68.23 (± 8.32)
years) positive for SNP was performed, according to their pre-test
probability of malignancy determined by the presence of risk factors
such as smoking, occupational exposure, previous cancer and pulmonary disease (COPD, pulmonary fibrosis, emphysema). PET/CT
examinations were acquired according to international acquisition
procedure guidelines using a Discovery 710 PET/CT system (GE
Healthcare). 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 patient who underwent FDG-PET/CT, SPN
was found to be positive for malignancy in 89 cases (60.95%) at
cytopathological examination. Uptake was absent in 20 cases, moderate in 44 and high in 82. 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 significance
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 significantly 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-offs for semiquantitative
parameters, in terms of predictive values, have been found: a cut-off
of 3.625 of SUVmax has 86.6% sensitivity and 69.1% specificity;
SUVmean’s optimal cut-off is 2.51, with 79.1% sensitivity and 76.3%
specificity; an MTV cut-off of 2.55 shows 74.7% sensitivity and
70.9% specificity while a TLG’s cut-off of 11.8 shows 66% sensitivity and 83.6% specificity. Furthermore, it has been observed how
TLG values directly correlates with SUVmax, SUVmean and MTV:
indeed, by means of Spearman correlations, it was seen that an
increase in TLG consequently overlaps with an increase in SUVmax,
SUVmean and MTV.
Conclusions: The qualitative parameters, size and location of SPN do
not show statistical significance for predicting the risk of malignancy.
No correlations have been found between the pre-test probability of malignancy and the semiquantitative parameters. Instead semiquantitative parameters can have an important predictive role in patients
with SPN at 18F-FDG-PET/CT. Cut-offs for SUVmax (3.625), SUVmean (2.51), MTV (2.55) and TLG (11.8) show good sensitivity and
specificity. TLG has shown to be directly correlated to SUVmax and
SUVmean and could play an important predictive role in patients with
SPN at FDG-PET/CT as a predictive parameter for malignancy.