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

Purpose

Several studies showed potential for monitoring response to systemic therapy in metastatic colorectal cancer patients with ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Before ¹⁸F-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 ¹⁸F-FDG PET in colorectal liver metastases.

Methods

Twenty patients scheduled for liver metastasectomy underwent two ¹⁸F-FDG PET scans within 1?week. Bland-Altman analysis was performed to assess repeatability of SUV_max, SUV_mean, volume and TLG. Tumours were delineated using an adaptive threshold method (PET_SBR) and a semiautomatic fuzzy locally adaptive Bayesian (FLAB) delineation method.

Results

Coefficient of repeatability of SUV_max and SUV_mean were ～39 and ～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 PET_SBR, from coefficients of repeatability of over 85?% to 45?% and 57?% for volume and TLG, respectively. Glucose transporter 1 (GLUT1) expression correlated to the SUV_mean. Vascularity (CD34 expression) and tumour hypoxia (carbonic anhydrase IX expression) did not correlate with ¹⁸F-FDG PET parameters.

Conclusion

In conclusion, repeatability of SUV_mean and SUV_max 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 ¹⁸F-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.