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-ADC_mean (P = 0.003) and pre-D values (P = 0.024), and significantly higher post-f (P = 0.002), ΔADC_mean % (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.