Low Incidence of Esophageal Toxicity After Lung Stereotactic Body Radiation Therapy: Are Current Esophageal Dose Constraints Too Conservative?

PURPOSE:To explore and quantify the relationship between esophageal dose and toxicity in the setting of lung stereotactic body radiation therapy (SBRT). METHODS AND MATERIALS:This analysis was conducted on the basis of a prospective study of patients treated with SBRT at our institution from October 2004 to December 2015. Most patients were treated with 54 Gy/3 fractions, 48 Gy/4 fractions alternate days, or 60 Gy/8 fractions daily. Toxicity was prospectively graded using Common Terminology Criteria for Adverse Events version 3.0. Logistic regression was used to estimate the risk of esophageal toxicity as a function of radiation therapy dose, in 2-Gy-equivalent dose, using an α/β ratio of 3 Gy in the linear-quadratic model. RESULTS:A total of 632 patients were analyzed. The median follow-up was 20.8 months. Median overall survival was 35.3 months. The rate of late or acute grade ≥1 esophageal toxicity, including dysphagia, odynophagia, and esophagitis, was 3.3% (n = 21). The median (range) esophageal doses were 11.8 Gy (0.2-48.2 Gy), 10.34 Gy (0.17-44.5 Gy), and 9.63 Gy (0.08-43 Gy) for Dmax, D1cc, and D2cc, respectively. A 15% risk of esophageal toxicity was associated with a 2-Gy-equivalent dose of Dmax 141.6 Gy, D1cc 123.61 Gy, and D2cc 117.6 Gy. Of the 21 patients who experienced esophageal toxicity, only 1 patient had grade 3 toxicity, and the remainder had grade 2 or lower toxicity. CONCLUSIONS:The observed rate of toxicity was low, despite some patients receiving relatively high doses to the esophagus. A prospective study in a targeted population, for example patients with ultracentral tumors, may provide more accurate dose-toxicity parameters.