Evaluation of a New Visual Uptake Scoring Scale for 18F-fluorothymidine Positron Emission Tomography in the Diagnosis of Pulmonary Lesions

Purpose: The aim of this analysis was to evaluate a new visual scoring scale developed to facilitate the qualitative appraisal of lesion uptake on (18)F-fluorothymidine PET ((18)F-FLT-PET).

Methods: Sixty-two patients with a pulmonary lesion of unknown aetiology who had undergone an F-fluorodeoxyglucose-PET/computed tomography (CT) suspicious for malignancy prospectively underwent an (18)F-FLT-PET/CT. Three nuclear medicine physicians independently reviewed each (18)F-FLT-PET/CT scan with knowledge of the location of the pulmonary lesion but blinded to the final diagnosis. They scored the lesion (18)F-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 (SUV(mean)) and maximum (SUV(max)) 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, SUV(mean) and SUV(max) 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 SUV(mean) and SUV(max) (r=0.83 and 0.87, respectively) and described a logarithmic pattern in relation to SUV(mean) and SUV(max) (r =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 SUV(mean) (0.77; P=0.026) and SUV(max) (0.79; P=0.047).

Conclusion: The (18)F-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 (18)F-FLT-PET/CT in lung cancer diagnosis.