Optimal prophylactic para-aortic radiotherapy in locally advanced cervical cancer: anatomy-based versus margin-based delineation

Precise delineation of the para-aortic nodal region is critical for the optimal therapeutic ratio of prophylactic para-aortic radiotherapy. We aimed to evaluate the para-aortic control and patient-reported gastrointestinal toxicity in patients with locally advanced cervical cancer who received anatomy-based or margin-based prophylactic para-aortic radiotherapy.We analyzed 160 patients with locally advanced cervical cancer who received prophylactic extended-field radiotherapy between January 2014 and November 2019 at two tertiary centers. Para-aortic nodal regions were delineated based on the anatomic principle-based atlas or marginal expansion from the aorta and inferior vena cava. The Patient-Reported Outcome version of the Common Terminology Criteria for Adverse Events was used to assess acute gastrointestinal toxicity, and a score of ≥3 was defined as severe gastrointestinal toxicity.Seventy-six (47.5%) and 84 (52.5%) patients received anatomy-based and margin-based prophylactic para-aortic radiotherapy, respectively. The median follow-up was 40.1 months (IQR 25.5-58.9). Para-aortic nodal failures occurred in one (1.3%) patient in the anatomy-based para-aortic radiotherapy group and in one (1.2%) patient in the margin-based para-aortic radiotherapy group (p=1.00). There was no in-field or marginal para-aortic nodal failure. The 3-year para-aortic recurrence-free survival for anatomy-based and margin-based para-aortic radiotherapy was 98.6% and 98.8%, respectively (p=0.94). Patients who received anatomy-based para-aortic radiotherapy reported less severe acute gastrointestinal toxicity than those who received margin-based para-aortic radiotherapy (13.2% vs 29.8%, p=0.01). A comparison of gastrointestinal toxicities showed that patients who received anatomy-based para-aortic radiotherapy reported significantly less severe gastrointestinal toxicity than those who received margin-based para-aortic radiotherapy in terms of frequency of diarrhea (7.9% vs 20.2%, p=0.03), severity of abdominal pain (3.9% vs 14.3%, p=0.03), and interference of abdominal pain (2.6% vs 11.9%, p=0.03).Anatomy-based prophylactic para-aortic radiotherapy achieved excellent para-aortic control and a lower incidence of severe patient-reported gastrointestinal toxicity. These findings suggest that anatomy-based delineation optimizes clinical outcomes of prophylactic para-aortic radiotherapy in locally advanced cervical cancer.