Local recurrence in rectal cancer: anatomic localization and effect on radiation target.

Purpose: To determine the sites of local recurrence after total mesorectal excision for rectal cancer in an effort to optimize the radiation target.

Methods And Materials: A total of 155 patients with recurrence after abdominal resection for rectal cancer were identified from a population-based consecutive cohort of 2,315 patients who had undergone surgery by surgeons trained in the total mesorectal excision procedure. A total of 99 cross-sectional imaging studies were retrieved and re-examined by one radiologist. The clinical records were examined for the remaining patients.

Results: Evidence of residual mesorectal fat was identified in 50 of the 99 patients. In 83 patients, local recurrence was identified on the imaging studies. All recurrences were within the irradiated volume if the patients had undergone preoperative radiotherapy or within the same volume if they had not. The site of recurrence was in the lower 75% of the pelvis, anatomically below the S1-S2 interspace for all patients. Only 5 of the 44 recurrences in patients with primary tumors >5 cm from the anal verge were in the lowest 20% of the pelvis. Six recurrences involved the lateral lymph nodes.

Conclusion: These data suggest that a lowering of the upper limit of the clinical target volume could be introduced. The anal sphincter complex with surrounding tissue could also be excluded in patients with primary tumors >5 cm from the anal verge.