Selection of rectal cancer patients for organ preservation after neoadjuvant therapy: value of T2W-MRI signal intensity

Background: Organ preservation strategies have been widely implemented for rectal cancer (RC) patients with a good response after neoadjuvant chemoradiation (nCRT). However, to accurately select eligible patients remains one of the key diagnostic challenges. Purpose: To identify eligible candidates for organ preservation after nCRT in RC, by identifying luminal response and lymph node metastases, based on T2W-MRI signal intensities. Material and Methods: A total of 171 RC patients underwent MRI before and after nCRT. The primary tumor (pre-nCRT-MRI) and tumor remnant (post-nCRT-MRI) were manually delineated. Ten signal intensity features were extracted and delta features were calculated by subtraction. Histopathological evaluation classified patients as lymph node negative (ypN0) or positive (ypN+), and as good responders (GR) or partial/poor responders (PR). Five models were constructed based on the timing of imaging. Results: 42/170 (25%) patients had ypN+, and 72/152 (47%) patients were considered GR. Univariate analysis showed 13/40 signal intensity features were significantly different between luminal response groups and 4/40 between nodal response groups. In multivariate analysis, the Baseline + Restaging-model yielded the best results for both luminal and nodal response with AUCs in the test set of 0.81 (95% CI=0.67–0.95) and 0.74 (95% CI=0.59–0.90), respectively. To identify PR, the Delta-model yielded an AUC of 0.72 (95% CI=0.56–0.89) and the Delta + Restaging-model an AUC of 0.81 (95% CI=0.67–0.95), both were not able to differentiate nodal response. The models including solely baseline or restaging features were not predictive. Conclusion: T2W-MRI signal intensities of the primary rectal tumor are related to the luminal and nodal response after nCRT and hold promise to identify patients eligible for organ preservation.