Simultaneous integrated boost to lateral pelvic lymph nodes during chemoradiotherapy in high-risk rectal cancer.

Abstract

Background: Preoperative chemoradiotherapy combined with total mesorectal excision (TME) is a standard treatment for locally advanced rectal cancer (LARC). However, lateral pelvic lymph nodes (LPLNs) are often inadequately treated with standard regimens. This study examines the treatment and postoperative outcomes in LARC patients receiving a simultaneous integrated boost (SIB) for LPLNs during long-course chemoradiotherapy.

Methods: This retrospective study included high-risk LARC patients (UICC, "Union Internationale Contre le Cancer", stage III) treated with preoperative chemoradiotherapy and SIB to LPLNs. Radiotherapy was delivered to the primary tumor and elective volumes with 50.4 Gy in 28 fractions, and an SIB with a median dose of 60.2 Gy was administered to clinically positive LPLNs. TME quality and postoperative complications were assessed using MERCURY and Clavien-Dindo, respectively. Time-to-event data were analyzed according to Kaplan-Meier.

Results: Between 2019 and 2023, 27 patients with high-risk LARC and LPLN metastases were treated with chemoradiotherapy. After a median follow-up of 19 months, 2‑year overall survival was 80%, disease-free survival 80%, and local control of dose-escalated lymph nodes 100%. Three patients were managed nonoperatively after a clinical complete response on endoscopy and imaging. Of the 22 patients who had surgery, only one had complications higher than Clavien-Dindo grade I; TME was graded as MERCURY I in 73%.

Discussion and conclusion: The SIB approach for LPLNs in LARC is feasible, does not increase postoperative morbidity, and achieves excellent local control. This study supports the consideration of dose-escalated radiotherapy for LPLNs to address high local recurrence risks.