The Effect Of Omitting The Ischiorectal Fossa From The Clinical Target Volume For Neoadjuvant Chemoradiotherapy In Resectable Advanced Lower Rectal Cancer

Several researchers suggest to omit the ischiorectal fossa (IRF) from clinical target volume (CTV) when rectal tumors are located less than 6 cm from the anal verge. The aim of this study was to explore whether omitting the IRF for neoadjuvant chemoradiation (NCRT) in resectable advanced lower rectal cancer could carry a lower incidence of perineal wound complications after abdomino-perineal resection (APR) without increasing local recurrence rate. We retrospectively identified 227 patients with advanced lower rectal cancer who underwent intensity-modulated radiation therapy (IMRT) and concurrent capecitabine following APR from 2009-2015. Total dose was 50.6 Gy (gross tumor volume, GTV) / 41.8 Gy (CTV) / 22 fractions. Thirteen patients were excluded for loss of follow-up or malignant tumor history. Ninety patients received IRF irradiation (IIRF group) and 124 patients did not (NIIRF group). Perineal recurrence rate, local recurrence free survival (LRFS), disease-free survival (DFS), overall survival (OS) were evaluated using Kaplan-Meier method. Patterns and Clavien-Dindo classification system of perineal wound complications after APR were compared between the two groups. Death risk was tested using Cox regression. Risk factors for perineal wound complications were identified using logistic regression. The median follow-up time were 26 months (13-57 months) (IIRF group) vs 44 months (9-60 months) (NIIRF group). The two groups had similar demographics, including gender, age, BMI, ECOG, T and N stage. The perineal recurrence rate, 3-year LRFS, DFS, OS in the IIRF group vs NIIRF group were 4.4% vs 2.4% (P=0.67), 88.4% vs 95.0% (P=0.08), 60.5% vs 78.8% (P=0.03), 83.1 % vs 89.5% (P=0.08), respectively. In Cox multivariate models, BMI<18.5kg/m2 (HR=4.32, 95% CI: 1.10-16.99), positive lymphovascular invasion (HR=11.30, 95% CI: 1.86-68.69) and distant metastasis (HR=8.88, 95% CI: 3.42-23.04) were correlated with OS. Perineal wound complications were 40.0% (IIRF group) vs 24.2% (NIIRF group) (P=0.01). Patterns and incidence of perineal wound complications of the two groups were counted: infection (23.3% vs 14.5%), sinus/fistula (1.1% vs 2.4%), dehiscence (1.1% vs 0.8%), healing delayed (11.1% vs 3.2%), hematoma/seroma (3.3% vs 4.0%). All severe perineal wound complications (≥grade 3) occurred in IIRF group (4.4%). In NIIRF group, grade 2 complications were recorded in 0.8% patient, and the rest was grade 1. Multivariate analysis showed irradiation of IRF (OR=2.88; 95%CI: 1.47-5.66), anemia (OR=3.40; 95%CI: 1.20-9.59), operation time > 180 mins (OR=2.43; 95%CI: 1.24-4.74), the interval between radiation therapy and surgery >8 weeks (OR=2.89; 95%CI: 1.45-5.75) were significantly related to perineal wound complications. Omitting the IRF from CTV for NCRT in resectable advanced lower rectal cancer could carry a lower incidence of perineal wound complications after APR without increasing local recurrence rate or reducing the LRFS and OS.