Reproducibility of depth of extramural tumor spread and distance to circumferential resection margin at rectal MRI: enhancement of clinical guidelines for neoadjuvant therapy.

OBJECTIVE The purpose of this study was to evaluate the reproducibility of measurements of minimal distance from an invasive tumor to the anticipated circumferential resection margin in prediction of depth of extramural tumor spread in patients with rectal cancer. MATERIALS AND METHODS Images from 168 consecutive pelvic MRI examinations of patients with rectal cancer were evaluated by radiologists at five imaging centers, by two expert reviewers, and by a resident. For each tumor, the minimal distance from the tumor to the circumferential resection margin and the maximum extramural tumor spread were evaluated by the observers. Tumors were classified into early (≤ 5 mm invasion) and advanced (> 5 mm invasion), and margin status was evaluated at the 1- and 5-mm levels. RESULTS There was good to very good agreement in classifying tumors as early and advanced (κ = 0.65-0.87), moderate to good agreement concerning circumferential resection margin status at the 1-mm level (k = 0.51-0.76), and fair to good agreement concerning circumferential resection margin status at the 5-mm level (k = 0.37-0.70). It was significantly easier to obtain agreement on the division into early and advanced tumors than on margin status at the 5-mm level for both the hospitals (p = 0.043) and the resident (p = 0.024). CONCLUSION Measurements of extramural tumor spread are more reproducible among different observers than are 5-mm distance measurements to the anticipated circumferential resection margin. This factor should be taken into account in the preparation and implementation of guidelines for neoadjuvant therapy for rectal cancer.