Accuracy of MRI for predicting the circumferential resection margin, mesorectal fascia invasion, and tumor response to neoadjuvant chemoradiotherapy for locally advanced rectal cancer.

Purpose: To evaluate the diagnostic accuracy of MRI for predicting the circumferential resection margin (CRM), mesorectal fascia (MRF) invasion, and the tumor response to neoadjuvant chemoradiotherapy (CRT) for locally advanced rectal cancer.

Materials And Methods: Sixty-five consecutive patients with locally advanced rectal cancer (> or =T3 or lymph node-positive) who underwent neoadjuvant CRT and subsequent surgery were enrolled in this retrospective study. Two blinded radiologists independently reviewed both the pre- and post-CRT rectal MR images and measured the post-CRT CRM; they recorded their confidence level with respect to the MRF invasion and tumor response using a 5-point scale. The diagnostic accuracy of each reviewer was calculated using receiver operating characteristic curve (ROC) analysis.

Results: The measured CRM was not significantly different from the reference standard (mean difference, -1.4 mm; 95% limits of agreement, -8.3-5.4 mm; interclass correlation coefficient, 0.82). The diagnostic accuracy (A(z)) for determining MRF invasion was 0.890 for reviewer 1 (95% confidence interval [CI], 0.788-0.954) and 0.829 for reviewer 2 (95% CI, 0.715-0.911). The A(z) for predicting complete or near-complete regression was 0.791 for reviewer 1 (95% CI, 0.672-0.882) and 0.735 for reviewer 2 (95% CI, 0.611-0.837).

Conclusion: MRI provides accurate information regarding the CRM of locally advanced rectal cancer after neoadjuvant CRT; it also shows relatively high accuracy for predicting MRF invasion and moderate accuracy for assessing tumor response.