Quantitative intravoxel incoherent motion parameters derived from whole‐tumor volume for assessing pathological complete response to neoadjuvant chemotherapy in locally advanced rectal cancer

Background Many locally advanced rectal cancer (LARC) patients can benefit from neoadjuvant chemotherapy (NACT), with some achieving a pathological complete response (pCR). However, there is limited research reporting on the value of intravoxel incoherent motion (IVIM) in monitoring pCR in patients with LARC. Purpose To identify whether IVIM parameters derived from whole‐tumor volume (WTV) before and after NACT could accurately assess pCR in patients with LARC. Study Type Prospective patient control study. Population Fifty‐one patients with LARC before and after NACT, prior to surgery. Field Strength/Sequence IVIM‐diffusion imaging at 3T. Assessment Apparent diffusion coefficient (ADC), slow diffusion coefficient (D), fast diffusion coefficient (D*), and perfusion‐related diffusion fraction (f) values were obtained on diffusion‐weighted magnetic resonance images (DW‐MRI) using WTV methods and calculated using a biexponential model before and after NACT. Statistical Tests DWI‐derived ADC and IVIM‐derived parameters and their percentage changes (ΔADC%, ΔD%, ΔD*%, and Δf%) were compared using independent‐samples t‐test and Mann–Whitney U‐test between the pCR and non‐pCR groups. The diagnostic performance of IVIM parameters and their percentage changes were evaluated using receiver operating characteristic curves. Results Compared with the non‐pCR group, the pCR group exhibited significantly lower pre‐ADCmean (P = 0.003) and pre‐D values (P = 0.024), and significantly higher post‐f (P = 0.002), ΔADCmean% (P = 0.002), ΔD% (P = 0.001), and Δf% values (P = 0.017). Receiver operating characteristic curves showed that the pre‐D value had the best specificity (95.12%) and accuracy (86.27%) in predicting the pCR status, and ΔD% had the highest area under the curve (0.832) in assessing the pCR response to NACT. Data Conclusions The IVIM‐derived D value is a promising tool in predicting the pCR status before therapy. The percentage changes in D values after therapy may help assess the pCR status prior to surgery. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017.