Esophageal tolerance to high-dose stereotactic ablative radiotherapy

Dose-volume parameters are needed to guide the safe administration of stereotactic ablative radiotherapy (SABR). We report on esophageal tolerance to high-dose hypofractionated radiation in patients treated with SABR. Thirty-one patients with spine or lung tumors received single- or multiple-fraction SABR to targets less than 1 cm from the esophagus. End points evaluated include D5cc (minimum dose in Gy to 5 cm3 of the esophagus receiving the highest dose), D2cc, D1cc, and Dmax (maximum dose to 0.01 cm3). Multiple-fraction treatments were correlated using the linear quadratic and linear quadratic-linear/universal survival models. Three esophageal toxicity events occurred, including esophagitis (grade 2), tracheoesophageal fistula (grade 45), and esophageal perforation (grade 45). Chemotherapy was a cofactor in the high-grade events. The median time to development of esophageal toxicity was 4.1 months (range 0.66.1 months). Two of the three events occurred below a published D5cc threshold, all three were below a D2cc threshold, and one was below a Dmax threshold. We report a dosimetric analysis of incidental dose to the esophagus from SABR. High-dose hypofractionated radiotherapy led to a number of high-grade esophageal adverse events, suggesting that conservative parameters to protect the esophagus are necessary when SABR is used, especially in the setting of chemotherapy or prior radiotherapy.