Introduction: The aim of this study was to evaluate tumor response using fluorine-18-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) in patients who received yttrium-90 selective internal radiation therapy (SIRT) for colorectal liver metastases. The initial and sixth-week tumor lesion glycolysis values were calculated to evaluate the success of the treatment and compare it with patient survival.
Materials and methods: Thirty-five patients (15 female, 20 male, mean age: 61.9 ± 9.0 years, range: 33-76 years) who received SIRT treatment for unresectable colorectal cancer liver metastases in our hospital between June 2008 and May 2011 were included in the study. All patients included in the study had liver-only or liver-dominant disease. The treatment response was evaluated by 18F-FDG PET/CT in the sixth week after treatment. Response was evaluated according to the change in total lesion glycolysis (ΔTLG). The ΔTLG was calculated using the following formula: ΔTLG=100 ×[standardized uptake value (SUV) mean1 × total functional tumor volumes (FTVs)1-SUV mean2 × FTV2]/SUV mean1 × FTV1.
Results: Mean FTV1 and FTV2 values were calculated to be 235.7 ± 203 and 107.3 ± 67 mm3, respectively (P=0.04). The mean ΔTLG was 43 ± 35 (range: 0-100). Mean overall survival time was 12.7 ± 8.0 months (range: 3-31 months). The cutoff value of ΔTLG was calculated to be 26.5 using receiver operating characteristic analysis (sensitivity 64%; specificity 85%; AUC=0.717 ± 0.087, P=0.034). Patients were allocated into those having values greater than the cutoff value (group 1) and those having values lower than the cutoff value (group 2) in order to calculate the effect of ΔTLG on survival. Survival was 11.32 ± 1.18 (95% CI 9.02-13.62) months in group 2 and 20.76 ± 2.71 (95% CI 15.46-26.06) months in group 1 (P=0.016). ΔTLG was found to be a significant factor in univariate analysis (P=0.01).
Conclusion: An 18F-FDG PET/CT scan with calculation of ΔSUVmax3, ΔFTV, and ΔTLG before and at the sixth week after SIRT may play an important role in evaluating early tumor response and survival expectancy in these patients and help decide whether these patients should be referred to other treatment modalities or to follow-up.