Performance of diffusion-weighted magnetic resonance imaging at 3.0T for early assessment of tumor response in locally advanced rectal cancer treated with preoperative chemoradiation therapy.

Abstract

The purpose of the article is to determine whether changes in apparent diffusion coefficient (ADC) values of locally advanced rectal cancer (LARC) obtained 2weeks after the beginning of chemoradiation therapy (CRT) allow to predict treatment response and whether correlate with tumor histopathologic response. Forty-three patients receiving CRT for LARC and 3.0T magnetic resonance imaging with diffusion-weighted sequences before treatment, 2weeks during, and 8weeks post the completion of CRT were included. ADC values were calculated at each time point and percentage of ADC changes at 2weeks (ΔADC during) and 8weeks (ΔADC post) were assessed. Data were correlated to surgical results and histopathologic tumor regression grade (TRG), according to Mandard's classification. ADC values and ΔADCs of complete responders (CR; TRG1) and non-complete responders (non-CR; TRG 2-5) were compared. Receiver-operating characteristic curve (ROC) analysis was used to assess diagnostic accuracy of ΔADC for differentiating CR from non-CR. The correlation with TRG was investigated using Spearman's rank test. ΔADC during and ΔADC post were significantly higher in CR (33.9% and 57%, respectively) compared to non-CR (13.5% and 2.2%, respectively) group (p=0.006 and p<0.001, respectively). ROC analysis revealed the following diagnostic performances: ΔADC during: AUC 0.78 (0.08), p=0.004, cut-off 20.6% (sensitivity 75% and specificity 76.5%); ΔADC post: AUC 0.94 (0.04), p≤0.001, cut-off 22% (sensitivity 95% and specificity 82.4%). Significant moderate and good negative correlation was found between ΔADC during and ΔADC post and TRG (r=-0.418, p=0.007; r=-694, p≤0.001, respectively). ΔADC at 2weeks after the beginning of CRT is a reliable tool to early assess treatment response.