Response assessment of locally advanced rectal cancer after neoadjuvant chemoradiotherapy: Is apparent diffusion coefficient useful on 3 T magnetic resonance imaging?

Abstract Aim To assess the diagnostic value of apparent diffusion coefficient (ADC) on 3 T device for the prediction of tumoral response to neoadjuvant chemoradiotherapy (nCRT) and for the response assessment after nCRT in patients with locally advanced rectal cancer (LARC), using pathology as a reference. Methods Forty‐one patients affected by LARC undergoing 3.0 T MRI before and after nCRT were retrospectively selected. After the conventional acquisition of high resolution T2‐weighted sequences, diffusion‐weighted MRI (DW‐MRI) was performed using a spin‐echo echo‐planar sequence with multiple b values (150, 500, 1000, 1500 s/mm 2 ). Fitted ADC values were calculated for each rectal lesion before and after nCRT by drawing a hand‐made region of interest (ROI) around the tumour outline. All patients underwent surgery and pathological staging (classified according to tumour regression grading [TRG] and to tumour and node [TN]) represented the reference standard. Pretreatment ADC value (pre‐ADC), ADC value obtained after nCRT (post‐ADC) and the difference between post‐ADC and pre‐ADC (ΔADC) were correlated with both the TRG classes and the TN staging system in each patient. Results The ADC values obtained in the post nCRT examination and the ΔADC were statistically related both to TRG ( p = 0.0004; p = 0.0126, respectively) and TN ( p = 0.0484; p = 0.0673, respectively) stages at histopathology. On the contrary, the pre‐ADC was not related either to the TRG classes or to the lesion TN staging system ( p > 0.05). Conclusions 3 T DW‐MRI using ADC value can be useful to assess the efficacy of nCRT in LARC; in fact, post‐ADC and ΔADC values improve MR capability to evaluate tumour response.