RESUMO
PURPOSE: To evaluate the efficacy of diffusion-weighted imaging (DWI) on 3 Tesla (T) MR imaging to predict the tumor response to neoadjuvant chemoradiation therapy (CRT) in patients with locally advanced rectal cancer. MATERIALS AND METHODS: Thirty-five patients who underwent neoadjuvant CRT and subsequent surgical resection were included. Tumor volume was measured on T2-weighted MR images before and after neoadjuvant CRT and the percentage of tumor volume reduction was calculated. The apparent diffusion coefficient (ADC) value was measured on the DWI before and after neoadjuvant CRT, and the change of ADC (Δ ADC) was calculated. The histopathologic response was categorized either as a responder to CRT or as a nonresponder. The relationship between the ADC parameters and the percentage of tumor volume reduction or histopathologic response was then evaluated. RESULTS: There was a significant correlation between tumor volume reduction and pre-CRT ADC and Δ ADC, respectively (r = -0.352, r = 0.615). Pre-CRT ADC of the histopathologic responders was significantly lower than that of the histopathologic nonresponders (P = 0.034). Δ ADC of the histopathologic responders was significantly higher than that of the histopathologic nonresponders (P < 0.005). CONCLUSION: DWI on 3T MR imaging may be a promising technique for helping to predict and monitor the treatment response to neoadjuvant CRT in patients with locally advanced rectal cancer.