An Observational Retrospective Study to See the Accuracy of Post-Neoadjuvant Radiotherapy MRI Staging in Cases of Rectal Cancers

Abstract Background Accurate restaging of rectal cancer following neoadjuvant radiotherapy (NART) is critical for determining appropriate surgical intervention. Magnetic resonance imaging (MRI) is widely used for this purpose, although its accuracy post-radiation is debated due to treatment-induced tissue changes. This is among the few Indian study validating MRI accuracy in post-NART rectal cancer staging. Aim To evaluate the diagnostic accuracy of MRI in restaging rectal cancer (T and N staging) post-NART by comparing it with postoperative histopathology. Methods This retrospective observational study included 28 patients treated with NART for rectal cancer between January 2020 and December 2024. MRI staging (6–8 weeks post-NART) was compared with final histopathology. T staging was dichotomized (T0–T2 vs T3–T4), and N staging as node-negative (N0) vs node-positive (N1–N2). Diagnostic measures (sensitivity, specificity, PPV, NPV) were calculated using histopathology as the reference standard. Results MRI accurately staged T in 11/28 (39.3%) and N in 10/27 (37.0%). T overstaging occurred in 53.6% and N overstaging in 40.7% of cases. Sensitivity was 48.1% (PPV 86.7%) for T staging and 52.2% (PPV 66.7%) for N staging. Specificity and NPV could not be reliably calculated due to the absence of true negatives in the cohort. Conclusion MRI demonstrates moderate sensitivity and high PPV for detecting residual tumor but frequently overestimates staging. MRI alone should not guide clinical decision-making post-NART. These findings reinforce the need for multimodal assessment rather than sole reliance on MRI.