PURPOSE: Clinical and dosimetric predictors of severe (grade 3 or greater) acute esophageal toxicity and subsequent esophageal dilation were explored in patients with limited-stage small cell lung cancer treated with accelerated hyperfractionated chemoradiation. METHODS AND MATERIALS: A total of 130 patients were identified who were treated to 45 Gy in 1.5-Gy twice-daily fractions with concurrent platinum-based chemotherapy between 2000 and 2009. Data on clinical, disease-related, and treatment-related variables were collected. Patients with percutaneous endoscopic gastrostomy tube insertion or intravenous hydration because of poor oral intake were designated as having acute grade 3 esophagitis. Univariate and multivariate analyses that associated treatment characteristics with esophagitis were assessed via logistic regression, and optimal cut points were identified with recursive partitioning analysis. RESULTS: Twenty-five patients developed severe acute esophagitis, at a rate of 26% (18/69) in patients treated with earlier 3-dimensional conformal radiation therapy techniques and 11.5% (7/61) in patients treated with intensity modulated radiation therapy techniques and omission of elective nodal irradiation. The incidence of esophageal stricture was 6% overall (8 of 128 eligible) but 26% (6/23) among those who experienced prior grade 3 acute esophagitis and 2% (2/105) among those with acute esophagitis less than or equal to grade 2. Significant multivariate predictors of acute esophagitis were mean dose and volume of esophagus receiving at least 5% to 35% of the prescribed dose (V5 to V40). Patients with V5 ≥ 74% had a 44.4% risk of severe acute esophagitis (12/27) versus 12.6% (13/103) among those with V5 < 74%. V45 was the only dosimetric predictor for esophageal stricture, with 13.7% of patients in whom V45 was ≥37.5% requiring subsequent dilation. CONCLUSIONS: Modern radiation techniques are associated with a lower frequency of severe acute esophagitis than previous paradigms. The proportion of esophagus receiving low- to moderate-range doses (mean, V5 through V40) predicts acute esophagitis, whereas the proportion of esophagus that receives high doses (V45) predicts the development of esophageal stricture that requires dilation. Patients who develop grade 3 acute esophagitis are at significant risk for subsequent esophageal stricture, whereas those with acute esophagitis of grade 2 or less display minimal risk.