Use of Specific Duodenal Dose Constraints During Treatment Planning Reduces Toxicity After Definitive Paraaortic Radiation Therapy for Cervical Cancer

Purpose: This study aimed to validate the safety of paraaortic nodal (PAN) radiation therapy (RT) for patients with cervical cancer when the duodenal dose is limited to V₅₅ < 15 cm³ and V₆₀ < 2 cm³. Methods and Materials: A total of 97 patients who were treated with RT for cervical cancer between 2010 and 2018 received at least 56 Gy to grossly involved PANs. Patients were treated with concurrent chemoradiation (n = 88; 91%), with 93% of patients (n = 90) receiving intensity modulated RT to the initial PAN field and 98% (n = 95) receiving intensity modulated RT to a sequential PAN boost. The V₅₅ < 15 cm³ and V₆₀ <2 cm³ criteria were implemented in 2014. Normal tissues were contoured on computed tomography (CT) simulation data sets, and the duodenum was contoured from the gastric outlet to the duodenojejunal flexure. Sixty-six patients (68%) had a resimulation scan after approximately 20 fractions. Composite duodenal doses were calculated using the initial CT scan for 50 patients (52%) and the resimulation CT scan for 47 patients (48%) depending on the anatomic changes throughout treatment. Results: The median duodenal V₅₅ was 3.5 cm³ (interquartile range [IQR], 0.2-8.1 cm³) and the median V₆₀ was 0.3 cm³ (IQR, 0.0-1.8). Constraints were exceeded in 18 patients, of whom 16 patients (89%) had been treated before 2014. Treatment for the 2 patients treated after 2014 was complicated by significant weight loss and reduced anterior-posterior diameter, which likely overestimated the true dose on the composite plan. Only 1 patient experienced grade 3 duodenal toxicity (stricture requiring endoscopic balloon dilation 3 months after treatment); however, the stricture was outside of the high-dose boost volume, and the patient had a history of gastritis. Six patients (6%) had a first recurrence within the PAN region. Conclusions: Limiting the duodenal dose to V₅₅ < 15 cm³ and V₆₀ < 2 cm³ for patients with cervical cancer and PAN involvement is feasible, and minimizes duodenal toxicity while maintaining acceptable local control rates.