Diffusion-weighted MRI in locally advanced rectal cancer : pathological response prediction after neo-adjuvant radiochemotherapy.

BACKGROUND AND PURPOSE

The aim of this study was to assess the predictive potential of diffusion-weighted magnetic resonance imaging (MRI) for the selection of favorable pathological responders after radiochemotherapy for locally advanced rectal cancer.

PATIENTS AND METHODS

In 59 patients with locally advanced rectal cancer, the apparent diffusion coefficient (ADC) in the tumor was obtained at 3 Tesla before radiochemotherapy and surgery. The predictive potential for pathological complete response (pCR) and good response (GR) was assessed. GR was defined as pCR and near-pCR based on the tumor regression grade.

RESULTS

The GR group consisted of 13 patients (22%) with 9 complete responders. Both the preradiochemotherapy ADC values and relative change in ADC (ΔADC) were predictive for pathological response. Preradiochemotherapy ADC values showed a positive predictive value of 42% for pCR and 67% for GR using a similar cut-off value of 0.97(*)10(-3) mm(2)/s. For ΔADC, the optimal threshold for predicting GR or pCR was a 41% increase of the ADC. With this threshold, positive predictive values of 64% and 91% were found for pCR and GR, respectively.

CONCLUSION

Low preradiochemotherapy ADC values and high ΔADC correspond to pathological good response. Diffusion-weighted MRI may be used as an additional tool for selecting good treatment responders after radiochemotherapy.