Purpose: The aim of this analysis was to evaluate a new visual scoring scale developed to facilitate the qualitative appraisal of lesion uptake on 18F-fluorothymidine PET (18F-FLT-PET).
Methods: Sixty-two patients with a pulmonary lesion of unknown aetiology who had undergone an 18F-fluorodeoxyglucose-PET/computed tomography (CT) suspicious for malignancy prospectively underwent an 18F-FLT-PET/CT. Three nuclear medicine physicians independently reviewed each 18F-FLT-PET/CT scan with knowledge of the location of the pulmonary lesion but blinded to the final diagnosis. They scored the lesion 18F-FLT uptake as follows: (0) no visible uptake; (1) <spleen; (2) ≥spleen, but <both liver and marrow; (3) between liver and marrow; (4) >liver and >marrow. Lesion mean (SUVmean) and maximum (SUVmax) standardized uptake values were measured in a separate session.
Results: In all, 35 lesions were malignant and 27 were benign, as assessed on the basis of surgery, biopsy or follow-up of at least 12 months. Visual score, SUVmean and SUVmax were statistically different between benign and malignant lesions. The visual scoring scale showed substantial to almost-perfect interobserver agreement with a weighted κ value of 0.84, 0.67 and 0.65 for each observer pair. The visual score was highly correlated to SUVmean and SUVmax (r=0.83 and 0.87, respectively) and described a logarithmic pattern in relation to SUVmean and SUVmax (r 2=0.67 and 0.72, respectively). The area under the receiver-operating characteristic curve for the visual score was 0.86 and was statistically different from that for SUVmean (0.77; P=0.026) and SUVmax (0.79; P=0.047).
Conclusion: The 18F-FLT scoring scale we propose is easy to use with high interobserver agreement and a significantly better discriminative capacity compared with SUV measurements. It has the potential to harmonize the qualitative interpretation of 18F-FLT-PET/CT in lung cancer diagnosis.