• locally advanced rectal cancer
• adc

Purpose
To evaluate the usefulness of the apparent diffusion coefficient (ADC) value at 3T-device in response assessment of locally advanced rectal cancer (LARC) after neoadjuvant chemoradiotherapy (n-CRT).

Materials and Methods
Thirty-seven patients affected by locally advanced rectal cancer underwent 3.0T MRI before and after n-CRT. After the preliminary acquisition of high resolution T2 weighted sequences, diffusion weighted MR images were performed using a spin-echo echo-planar sequence with multiple b-values (150, 500, 1000, 1500 sec/mm2) and an ADC map was obtained. Fitted ADC values were calculated for each rectal lesion before and after n-CRT, by drawing a hand-made ROI around the tumor outline. All patients underwent surgery and the pathologic staging (classified according to TNM and to TRG) represented the reference standard. Pre-treatment ADC value (p-ADC), ADC value obtained after n-CRT (n-ADC) and the difference between p-ADC and n-ADC (ΔADC) were correlated with both the TNM and the TRG staging systems, in each patient.

Results
The ADC value obtained in the post n-CRT examination was statistically related both to TRG and TNM stages at histopathology (p=0,0027; p=0,0165). Otherwise the ΔADC and the p-ADC values were not related to the pathologic staging.

Conclusions
DW-MRI, using ADC map and value, can be useful to assess the efficacy of n-CRT in LARC; in fact post- n-CRT ADC value improves the MR capability in the evaluation of n-CRT response assessment.