Value of diffusion-weighted MR imaging in assessing response of neoadjuvant chemo and radiation therapy in locally advanced rectal cancer

BackgroundRectal cancer is one of the most common tumors in industrialized countries and one of the most common malignant tumors of the gastrointestinal tract. MR imaging has become the most accurate technique in local staging of rectal cancer; this is due to advances in terms of imaging equipment, coils, and sequences that have progressively improved the technique, with a parallel increase in accuracy.ObjectiveTo assess the role of magnetic resonance imaging with diffusion in staging of rectal carcinoma before and after chemo and radiation therapy in relation to histopathological findings.Materials and methodsThe studied group included 19 patients proved to be rectal carcinoma by colonoscopy between October 2011 and December 2013. All patients were evaluated with conventional MRI and diffusion weighted images. Our population which was staged as Tx N2 M0 and T3–T4 Nx M0 stage, underwent MR and diffusion weighted imaging (DWI) before neoadjuvant chemo and radiation therapy and later 6–8 wks. After the end of the treatment they performed again MR for the re-staging of disease. The sensitivity, specificity and diagnostic accuracy for both examinations were calculated. Our gold standard was the histopathology.ResultsFor T stage conventional MRI showed 60% sensitivity and 33% specificity with overall diagnostic accuracy 46.5% which increased after adding DWI to 87% sensitivity and 80% specificity with an overall accuracy 83.5%. N stage prediction by conventional MRI was 74% sensitivity and 80% specificity with an overall accuracy 78%. This increased after adding DWI to 83% sensitivity and 83% specificity with an overall accuracy 83%. MRI with DWI showed diagnostic accuracy 94.7%, and without DWI the diagnostic accuracy was 84.2%.ConclusionThe use of additional DWI yields better diagnostic accuracy than does use of conventional MR imaging alone in the evaluation of complete response to neoadjuvant chemo radiotherapy in patients with locally advanced rectal cancer.