MRI for Response Evaluation after Chemoradiotherapy for Locally Advanced Rectal Cancer

Background: Standard treatment for T3 or T4 and/or node-positive rectal 
cancer is preoperative chemoradiotherapy (CRT) followed by total mesorectal 
resection (TME). After surgery, 10–24% of patients have no remaining tumor. 
Complete pathologic response (pCR) after CRT has led to nonoperative 
treatment for carefully chosen patients with a complete clinical response (CR). 
5-year overall survival (OS) and disease free survival (DFS) were 93% and 
85%. DWI can evaluate chemoradiotherapy response (8-10), adding DWI to 
regular MRI increased radiologists' ability to select full responders. 
Aim: The purpose of our study is to evaluate the accuracy of MRI for selection 
of complete responders after chemoradiotherapy for locally advanced rectal 
cancer. 
Subject and Methods: This is a retrospective study. Baseline, post treatment 
MRI scans, Clinical assessment including digital rectal examination, and 
endoscopy are needed for each patient.
Results: ADC after chemoradiotherapy in the study population ranged from 
0.43 to 1.53. T2WI volumetry after CRT in the study population ranged from 
3.1 to 8.7. Number of patients with good MRI - TRG in the study population 
was 20 (67%). 
Conclusion: Pathological and MRI evaluation agree well. DWI patterns and 
T2W MRI-based MR-TRG improve MRI's diagnostic effectiveness for 
predicting pathological response. Improves interobserver agreement and 
radiologist trust. Further studies are needed to investigate MRI-capacity TRG's 
to identify pathological complete responders for nonoperative therapy and to 
give complementary prognostic information to pathological TRG for risk-
stratification following surgery.