Dual point 18FDG PET/CT has been used for differentiation of inflammatory and malignant lung lesions, as it has been shown that FDG uptake increases in malignant cells. Nevertheless, the detection of a high FDG uptake (SUVmax >2.5) in a single acquisition can be enough to diagnose a malignant lung nodule and does not need further time consuming and radiation exposure procedures.
We performed dual point FDG-PET/CT in order to characterize undeterminable TC detected lung lesions and assess which group of lesions may be more appropriately selected for dual point imaging after the first scan.
From June 2013 to June 2014, 42 consecutive patients (median age 70 years) with 44 TC detected undeterminable lung lesions were submitted to dual point 18FDG-PET/CT. Lesion size varied from 9 to 94 mm (mean size 29.7 mm, median 25 mm). A visual and semi-quantitative evaluation (SUVmax) were obtained by two skilled nuclear physicians in agreement at 1 (early) and 2 hours (late) from 3.7 MBq/Kg of 18FDG e.v. injection. DeltaSUVmax (late SUVmax – early SUVmax/early SUVmax * 100) was then calculated. Final diagnosis was achieved with histopathological evaluation for 26, and with a 8 months median follow-up for 16 patients.
In our series we found 28 malignant lesions, 6 benign tumours and 10 inflammatory diseases. In small lesions (<= 2.5 cm), malignant nodules SUVmax was always >2.5 (2.6 – 10.2), benign tumours SUVmax varied from 1.4 to 2.4, and in flogistic diseases from 1.7 to 2.3 in early evaluation, whereas for larger lesions SUVmax varied from 3.9 to 17.7 in malignant nodules, and from 1.4 to 7.2 in benign and inflammatory disease. Median deltaSUVmax was 39%, 20% and 3% in malignant, benign and inflammatory diseases respectively. Nevertheless, in 3 out of 4 (75%) non malignant lesions with early SUVmax >=2.5, and in 3 out of 12 (25%) with early SUVmax <2.5, deltaSUV increased more than 14%. A Chi-square test applied for deltaSUVmax >20% revealed a statistical value both in differentiation between malignant and benign lesions (p<0,02), and between malignant and inflammatory disease (p<0,001), but not between benign and inflammatory (p<0,21). A deltaSUVmax >20% could differentiate malignant from inflammatory disease also for lesions <2.5 cm (p<0,02).
Our data confirm the different kinetics of FDG uptake in malignant, benign and inflammatory lung lesions, that could be used in disease differentiation. However, a high early FDG uptake and deltaSUV could not be exclusive of a malignant process in larger lesions. On the other hand, early PET/CT seems to be enough suitable in small lung lesions to differentiate malignant from inflammatory and benign processes, and dual-point imaging may be worthwhile just for improving specificity in small lesion with border-line SUVmax at early evaluation. Nevertheless, larger studies are necessary to confirm this hypothesis.

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