Dynamic contrast enhanced-MRI for the detection of pathological complete response to neoadjuvant chemotherapy for locally advanced rectal cancer

Objective To determine the ability of dynamic contrast enhanced (DCE-MRI) to predict pathological complete response (pCR) after preoperative chemotherapy for rectal cancer. Methods In a prospective clinical trial, 23/34 enrolled patients underwent pre- and post-treatment DCE-MRI performed at 1.5T. Gadolinium 0.1 mmol/kg was injected at a rate of 2 mL/s. Using a two-compartmental model of vascular space and extravascular extracellular space, Ktrans, kep, ve, AUC90, and AUC180 were calculated. Surgical specimens were the gold standard. Baseline, post-treatment and changes in these quantities were compared with clinico-pathological outcomes. For quantitative variable comparison, Spearman's Rank correlation was used. For categorical variable comparison, the Kruskal-Wallis test was used. P≤0.05 was considered significant. Results Percentage of histological tumour response ranged from 10 to 100%. Six patients showed pCR. Post chemotherapy Ktrans (mean 0.5 min-1 vs. 0.2 min-1, P= 0.04) differed significantly between non-pCR and pCR outcomes, respectively and also correlated with percent tumour response and pathological size. Post-treatment residual abnormal soft tissue noted in some cases of pCR prevented an MR impression of complete response based on morphology alone. Conclusion After neoadjuvant chemotherapy in rectal cancer, MR perfusional characteristics have been identified that can aid in the distinction between incomplete response and pCR.Key Points & Dynamic contrast enhanced (DCE) MRI provides perfusion characteristics of tumours. & These objective quantitative measures may be more helpful than subjective imaging alone & Some parameters differed markedly between completely responding and incompletely responding rectal cancers. & Thus DCE-MRI can potentially offer treatment-altering imaging biomarkers.