[Value of diffusion-weighted magnetic resonance imaging in prediction of the response to preoperative chemoradiotherapy in rectal carcinoma].

OBJECTIVE: To investigate the value of diffusion weighted imaging (DWI) in predicting the efficacy of preoperative chemoradiotherapy (CRT) for locally advanced rectal cancer. METHODS: From 2007 to 2012, 86 patients with histopathologicaIly proven rectal cancer who underent pre-CRT were enrolled in this study prospectively. Diffusion-weighted MRl was performed in all patients before pre-CRT, while it was performed in part of the patients during and after pre-CRT as well.ADC values of the tumors were calculated on the workstation. Patients were assigned to the tumor downstaged group or the tumor nondownstaged group on the basis of T staging. The change in ADC following treatment and the difference in ADC between groups were analyzed. RESULTS: Of the 86 patients after surgery, 20 were diagnosed with T0, 2 with T1, 17 with T2, 44 with T3 and 3 with T4. 39 patients were classified as the downstaged group, of which 18 were of pCR. The remaining 47 patients were classified as the nondownstaged group. Of the total of 86 patients, the mean ADC values before, during, and after pre-CRT (pre-ADC, during-ADC, and post-ADC) were (1.03±0.17)×10(-3), (1.39±0.28)×10(-3), and (1.61±0.27)×10(-3) mm(2)/s and there was a significant difference (P<0.001). However, the pre-CRT ADC of the downstaged group did not differ significantly from that of the nondownstaged group (P=0.615). Of the 43 patients who underwent MRI before, during and after pre-CRT, the mean ADC values were (1.05±0.16)×10(-3), (1.39±0.29)×10(-3)and (1.67±0.30)×10(-3) mm(2)/s, respectively, showing a significant difference (P<0.001)as well. CONCLUSIONS: The mean ADC value of rectal cancer is gradually increasing along with the course of chemotherapy. Pre-ADC is not a good parameter to be used to predict the efficacy of pre-CRT for locally advanced rectal cancer.