Excluding external iliac node irradiation during neoadjuvant radiotherapy decreases lower intestinal toxicity without compromising efficacy in T4b rectal cancer patients with tumours involving the anterior structures

Abstract

Abstract Background This study aimed to explore the impact of excluding the external iliac node (EIN) from the clinical target volume (CTV) during preoperative radiotherapy in T4b rectal cancer with anterior structure invasion. Methods We identified 132 patients with T4b rectal cancer involving the anterior structures who received radiotherapy followed by surgery between May 2010 and June 2019. Twenty-nine patients received EIN irradiation (EIN group), and 103 did not (NEIN group). Failure patterns, survival and toxicities were compared between the two groups. Multivariate Cox proportional hazard regression was used to analyse the factors affecting survival. Results A total of 132 patients with a median age of 55 years were included in the analysis, 94.7% patients were diagnosed as cN+. Distant failure occurred first in 24 patients (18.2%), and total distant metastasis were noted in 31 patients (23.5%). 11 patients (8.3%) developed locoregional recurrence, 10 (9.7%) patients were in the NEIN group, and 1 (3.4%) was in the EIN group (P = 0.34). The EIN region failure rate was seen in 1patient (1.0%) in the NEIN group and no patients in the EIN group. The locoregional recurrence-free survival (LRFS), distant metastasis-free survival (DMFS), overall survival (OS) and progression-free survival (PFS) rates were 96.3% vs. 90.5%, 82.1% vs.73.7%, 75.9% vs. 78.0% and 72.4% vs. 68.3% (all P > 0.05) for the EIN group and NEIN group, respectively. For patients with cN+, NEIN irradiation consistently did not decrease the LRFS, DMFS, OS and PFS compare to the EIN group. EIN irradiation failed to be an independent prognostic factor for LRFS, DMFS, OS and PFS. The incidence of grade 3–4 acute toxicity in the lower intestine was significantly higher in the EIN group than in the NEIN group (13.8% vs. 1.9%, P = 0.02). The Dmax (4479cGy vs. 5039cGy), V35 (45.8cc vs. 91.1cc) and V45 (11.4cc vs. 51.0cc) of the small bowel was decreased in the NEIN group compared to the EIN group. Conclusions Exclusion of the EIN from the CTV in T4b rectal cancer with anterior structure invasion could reduce lower intestinal toxicity without compromising oncological outcomes. These results need further evaluation in future studies.