Radiation Therapy Dose Escalation to Clinically Involved Pelvic Sidewall Lymph Nodes in Locally Advanced Rectal Cancer.

Purpose: Lateral pelvic sidewall lymph nodes (PSW LN) may be involved in up to 24% of locoregionally advanced rectal cancers. PSW LN are not resected in total mesorectal excision (TME), and no standard of care regarding the management of PSW LN exists in the United States. We assessed our institutional experience of preoperative radiation therapy (RT) boost to clinically involved PSW LN that were not planned for resection.

Methods And Materials: Data from all patients with rectal adenocarcinoma treated between 2006 and 2018 were reviewed to identify those who received a cumulative dose of >50.4 Gy to suspicious PSW LN during neoadjuvant chemoradiation therapy (nCRT). Demographic, cancer characteristic, treatment, and toxicity data were derived from the chart.

Results: Of a total of 261 patients, 12 patients met the inclusion criteria. The median age was 47.5 years, and 83% of patients were men. All patients had T3/4 disease, 17% of patients had N1b disease and the remainder had N2 disease, and 33% had M1 disease (all ≤2 metastases). Seventy-five percent of patients had moderately or poorly differentiated histology. The mean distance from the anal verge was 4.85 cm (range, 2-8.9 cm), and 58% had ≥2 PSW LN with an average short axis diameter of 1.11 cm (range, 0.4-3.2 cm). Boost doses ranged from 53.48 Gy to 60.2 Gy in 27 to 30 fractions (1.8-2.15 Gy/fraction). The median follow-up time was 18 months. One patient who received concurrent capecitabine and irinotecan had grade 3 perineal dermatitis and anemia during nCRT. The median hospitalization time for TME was 6.5 days. Within 90 days of TME, 1 patient required surgical exploration for perineal wound breakdown, and another required a blood transfusion for anemia. At the time of the last follow up, 75% of patients were alive. Local control at 12 months was 90%.

Conclusions: RT dose escalation to nonresected PSW LN during nCRT was well tolerated with a low risk of acute toxicity and perioperative complications and has a high rate of local control at 12 months. RT boost warrants further study in patients with clinically involved nonresected PSW LN.