Response assessment in rectal cancer undergoing total neoadjuvant therapy: decision tree analysis integrating contrast enhanced T1-weighted MRI.

BACKGROUND: This study assesses the role of contrast enhanced T1-weighted imaging (CE-T1WI) in improving response assessment for rectal cancer patients undergoing total neoadjuvant therapy (TNT) and its integration with T2-weighted imaging (T2WI) and DWI using decision tree analysis. METHODS: A retrospective analysis was conducted on rectal cancer patients between January 2020 and December 2022 who underwent TNT followed by MRI-based response assessment, including T2WI, DWI, and CE-T1WI. Complete response (CR) was defined as pathologic CR or sustained clinical CR for ≥2 years. Diagnostic performance was assessed using receiver operating characteristic analysis. Logistic regression was performed to identify predictors of CR. Finally, a decision tree model was constructed to determine the optimal combination of sequences for predicting CR. RESULTS: A total of 124 rectal cancer patients (mean age 58 ± 12 years; 89 men) were analyzed, of whom 45 (36%) achieved CR. CE-T1WI demonstrated superior predictive performance (AUC = 82.3% [75.0−88.7]) compared to DWI (78.6% [71.1−85.9]) and T2WI (74.5% [66.5−82.4]). In the two sequences combinations, the combination of DWI and CE-T1WI achieved the highest AUC of 82.9% (75.7−89.8), with an accuracy of 85.5% (79.0−91.9), sensitivity of 73.4% (60.0−86.0) and specificity of 92.4% (85.9−97.6), outperforming the other combinations. Finally, the decision tree model integrating three sequences achieved an AUC of 90.1% (83.7−95.6), with an accuracy of 86.4% (80.6−91.9), a sensitivity of 77.6% (62.5−91.8) and a specificity of 91.2% (81.7−97.6). CONCLUSION: Integrating CE-T1WI with other sequences enhances CR prediction in rectal cancer patients undergoing TNT, supporting its inclusion in routine MRI for improved response assessment.