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

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 (delta ADC) 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 delta ADC were sta-tistically 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 delta ADC values improve MR capability to evaluate tumour response.