Predicting high-grade esophagus toxicity after treating central lung tumors with stereotactic radiotherapy using a Normal Tissue Complication Probability model

Abstract Background The treatment of central lung tumors with Stereotactic Body Radiotherapy (SBRT) is challenged by the risk of excessive esophageal toxicity. To improve clinical decision making we aimed to derive Normal Tissue Complication Probability (NTCP) models in a patient cohort with central lung tumors treated with SBRT and to evaluate the currently used esophagus dose-constraints. Material and Methods Patients with a central lung tumor who received SBRT (8 fractions of 7.5 Gy or 12 fractions of 5 Gy) were included. Doses were recalculated to an equivalent dose of 2 Gy (EQD2Gy) with an α/β-ratio of 10 Gy for acute and 3 Gy for late toxicity (cut-off was 3 months). The esophagus was manually delineated. NTCP modelling based on logistic regression was used to relate dose-volume histogram (DVH) parameters (Dmax, D1cc, D2cc, D5cc) to acute and late toxicity. Parameters with a p-value Results For this study, 188 patients with 203 tumors were eligible. Esophagus toxicity occurred in 33 patients (18%). Late high-grade toxicity consisted of two possible treatment-related deaths (grade 5) and two patients with grade 3 toxicity. Acute toxicity only consisted of grade 1 (n = 19) and grade 2 toxicity (n = 10). All investigated DVH-parameters were significantly correlated to acute and late toxicity. The probability of late high-grade toxicity is 1.1% for 8 fractions and 1.4% for 12 fractions, when applying the current dose-constraints. Conclusion High-grade esophageal toxicity occurred in 2.1% of the patients including two possible treatment-related deaths. The currently used dose-constraints correspond to a low risk of high-grade toxicity.