Intravoxel incoherent motion diffusion-weighted imaging for discriminating the pathological response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer

Abstract

To investigate the usefulness of intravoxel incoherent motion diffusion-weighted imaging (IVIM-DWI) in discriminating the pathological complete response (PCR) to neoadjuvant chemoradiotherapy (nCRT) in locally advanced rectal cancer (LARC), 42 patients underwent preoperative IVIM-DWI before (pre-nCRT) and after nCRT (post-nCRT). The values of pre-nCRT and post-nCRT IVIM-DWI parameters (ADC, D, D and f), together with the percentage changes (δ% parametric value) induced by nCRT, were compared between the PCR (tumour regression grade [TRG] 4) and non-PCR (TRG 0, 1, 2 or 3) groups and between the GR (TRG 3 or 4) and PR (TRG 0, 1 or 2) groups based on the Dworak TRG system. After nCRT, the ADC and D values for LARC increased significantly (all P < 0.05). The TRG score revealed a positive correlation with pref (r = 0.357, P = 0.020), postD (r = 0.551, P < 0.001) and δ%D (r = 0.605, P < 0.001). The PCR group (n = 10) had higher preD, pref, postD, δ%ADC and δ%D values than the non-PCR group (n = 32) (all P < 0.05). The GR group (n = 15) exhibited higher postD, δ%ADC and δ%D values than the PR group (n = 27) (all P < 0.05). Based on ROC analysis, δ%D had a higher area under the curve value than δ%ADC (P = 0.009) in discriminating the PCR from non-PCR groups. In conclusion, IVIM-DWI may be helpful in identifying the PCR to nCRT for LARC and is more accurate than traditional DWI.