Esophagus toxicity after stereotactic and hypofractionated radiotherapy for central lung tumors: Normal tissue complication probability modeling

Purpose: To correlate esophagus toxicity and dose-volume histogram (DVH) parameters in order to assess risks, and derive a Normal Tissue Complication Probability (NTCP) model. Methods and materials: Patients with a central lung tumor from 2 centers, who underwent stereotactic or hypofractionated radiotherapy (≤12 fractions), were analyzed. Doses were recalculated to an equivalent dose of 2 Gy with an α/β ratio of 10 (EQD₂ ¹⁰). The esophagus was manually delineated and DVH-parameters (D_max,EQD2, D_1cc,EQD2, D_2cc,EQD2, D_5cc,EQD2) were analyzed and used for NTCP modeling based on logistic regression analysis. Results: Two-hundred-and-thirty-one patients with 252 tumors were eligible. No acute or late grade 3–5 esophageal toxicity was reported. Acute grade 1–2 esophagus toxicity was recorded in 38 patients (17%). All DVH-parameters were significantly higher in patients with toxicity. NTCP models showed a 50% probability of acute grade 1–2 toxicity at a D_max of 67 Gy EQD₂ ¹⁰ and D_1cc of 42 Gy EQD₂ ¹⁰. No difference in overall survival was observed between patients with and without toxicity (p = 0.428). Conclusion: As no grade 3–5 esophageal toxicity was observed in our cohort, a D_max of 56 Gy EQD₂ ¹⁰ and a D_5cc of 35.5 Gy EQD₂ ¹⁰ could be delivered without high risks of severe toxicity. The NTCP models of this study might be used as practical guidelines for the treatment of central lung tumors with stereotactic radiotherapy.