Variability of total lesion glycolysis by 18F-FDG-positive tissue thresholding in lung cancer

The aim of this work was to assess the variability of total lesion glycolysis (TLG) measurements in lung cancer patients, obtained with fixed percentages of the maximum standardized uptake value (SUVmax) thresholds.

Thirteen lesions (10 patients) were analyzed in 10 successive 2.5-min frames of an (18)F-FDG PET dynamic acquisition obtained between 60 and 110 min after injection. (18)F-FDG-positive lesion volume, associated average SUV (SUVmean), and TLG (volume × SUVmean) were assessed in each frame using thresholds of 40%, 50%, 60%, 70%, and 80%. For each threshold, the average relative SD of TLG, leading to relative measurement error and repeatability, was calculated over the lesion series. The dependence of TLG variability on volume and SUVmean variability was also assessed.

The average relative SD of TLG correlated strongly with threshold: 1.0866 × exp(0.0472 × threshold) (r = 0.999; P < 0.01). For the 40% threshold, average TLG over the series was 225.9 g (range, 41.7-1,086.3), relative measurement error and repeatability were 14.5%-20.4% (95% confidence interval), and no significant difference was found between TLG and volume variability. For the other thresholds, TLG variability was significantly lower or greater than volume or SUVmean variability, respectively.

In current clinical practice, a formula allows quick estimation of TLG variability for any percentage of the SUVmax threshold: the higher the threshold the greater the TLG variability.