Response to Chemotherapy in Gastric Adenocarcinoma With Diffusion-Weighted MRI and 18F-FDG-PET/CT: Correlation of Apparent Diffusion Coefficient and Partial Volume Corrected Standardized Uptake Value With Histological Tumor Regression Grade

Purpose: To assess whether changes in diffusion-weighted MRI (DW-MRI) and F-18-fluoro-2-deoxyglucose positron emission tomography/computed tomography (F-18-FDG PET/CT), correlate with treatment response to neoadjuvant therapy (NT), as expressed by tumor regression grade (TRG), from locally advanced gastric adenocarcinoma (GA). Materials and Methods: Seventeen patients underwent both DW-MRI and F-18-FDG-PET/CT scans before and after the end of NT. Apparent diffusion coefficient (ADC) and mean standardized uptake value (SUV) corrected for partial volume effect (PVC-SUVBW-mean) were evaluated and compared with histopathological TRG. Results: Pre-and post-NT and percentage changes for ADC and PVC-SUVBW-mean were assessed. Post-NT ADC and DADC showed a significant inverse correlation with TRG (r= -0.71; P = 0.0011 and r = -0.78; P = 0.00020, respectively) and significant differences in their mean values were found between responders (TRG 1-2-3) and nonresponders (TRG 4-5) (P = 0.0009; P = 0.000082, respectively). No correlations with TRG were found for pre-NT ADC and for all PVC-SUVBW-mean values as well as between Delta ADC and Delta PVC-SUVBW-mean. Conclusion: DW-MRI seems more accurate than 18 FFDG-PET/CT and ADC modifications may represent a reproducible tool to assess tumor response for GA.