Stereotactic body radiotherapy (SBRT) to central lung tumors can cause esophageal toxicity, but little is known about the incidence or risk factors. We reviewed central lung SBRT patients to identify dosimetric factors predictive of esophageal toxicity.

We assessed esophageal toxicity in 125 SBRT patients. Using biological equivalent doses with α/β=10 Gy (BED₁₀), dose-volume histogram variables for the esophagus (Dv and Vd) were assessed for correlation with grade ⩾2 acute toxicity.

Incidence of grade ⩾2 acute toxicity was 12% (n=15). Highly significant logistic models were generated for D₅cc and Dmax (p<0.001). To keep the complication rate <20%, the model requires that D₅cc⩽26.3 BED₁₀. At 2 years, the probability of complication with BED₁₀D₅cc>14.4 Gy was 24%, compared to 1.6% if ⩽14.4 Gy.

This novel analysis provides guidelines to predict acute esophageal toxicity in lung SBRT. Dose to the hottest 5cc and Dmax of the esophagus were the best predictors of toxicity. Converting the BED₁₀ limits to physical doses, D₅cc to the esophagus should be kept less than 16.8, 18.1 and 19.0 Gy for 3, 4, and 5 fractions, respectively, to keep the acute toxicity rate <20%.