Reproducibility of functional volume and activity concentration in 18F-FDG PET/CT of liver metastases in colorectal cancer

Several studies showed potential for monitoring response to systemic therapy in metastatic colorectal cancer patients with F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET). Before F-18-FDG PET can be implemented for response evaluation the repeatability should be known. This study was performed to assess the magnitude of the changes in standardized uptake value (SUV), volume and total lesion glycolysis (TLG) in colorectal liver metastases and validate the biological basis of F-18-FDG PET in colorectal liver metastases. Twenty patients scheduled for liver metastasectomy underwent two F-18-FDG PET scans within 1 week. Bland-Altman analysis was performed to assess repeatability of SUVmax, SUVmean, volume and TLG. Tumours were delineated using an adaptive threshold method (PETSBR) and a semiautomatic fuzzy locally adaptive Bayesian (FLAB) delineation method. Coefficient of repeatability of SUVmax and SUVmean were similar to 39 and similar to 31 %, respectively, independent of the delineation method used and image reconstruction parameters. However, repeatability was worse in recently treated patients. The FLAB delineation method improved the repeatability of the volume and TLG measurements compared to PETSBR, from coefficients of repeatability of over 85 % to 45 % and 57 % for volume and TLG, respectively. Glucose transporter 1 (GLUT1) expression correlated to the SUVmean. Vascularity (CD34 expression) and tumour hypoxia (carbonic anhydrase IX expression) did not correlate with F-18-FDG PET parameters. In conclusion, repeatability of SUVmean and SUVmax was mainly affected by preceding systemic therapy. The repeatability of tumour volume and TLG could be improved using more advanced and robust delineation approaches such as FLAB, which is recommended when F-18-FDG PET is utilized for volume or TLG measurements. Improvement of repeatability of PET measurements, for instance by dynamic PET scanning protocols, is probably necessary to effectively use PET for early response monitoring.