Analysis of related factors of radiation pneumonitis after radiotherapy for thoracic segment esophageal cancer

Objective: To investigate the effects of clinical characteristics, irradiation techniques and dose-volume parameters on radiation pneumonitis (RP) in thoracic segment esophageal cancer patients, so as to provide reference for the formulation of radiotherapy protocol for thoracic esophageal cancer. Methods: The incidence of RP in 247 patients with thoracic segment esophageal cancer from June 2014 to June 2019 was analyzed retrospectively, then univariate and multivariate analyses were performed on the clinical characteristics, radiation techniques and lung dosimetry parameters of these patients. The area under receiver operating characteristic (ROC) curve was used to verify the diagnostic efficacy of RP ≥ grade 1, ≥ grade 2 and ≥ grade 3. Results: There were 118 cases (47.8%) with RP ≥ grade 1, 54 cases (21.9%) with RP ≥ grade 2, 17 cases (6.9%) with RP ≥ grade 3. The result of univariate analysis showed that lung V₅-V₄₀ and MLD were both related to the occurrence of RP ≥ grade 1 (Z = -5.802 to -4.306, P < 0.05). ≥ grade 2, and ≥ grade 3, respectively (F = 0.057 to 11.616, 0.087 to 3.392, P < 0.05). GTV volume, PTV volume, GTV/lung volume (%) and PTV/lung volume (%) were related to RP ≥ grade 1(Z = -3.377 to -2.041, P < 0.05) and RP ≥ grade 2 (F = 3.600 to 9.801, P < 0.05). Smoking index > 400 was significantly correlated with RP ≥ grade 3 (X² = 13.295, P < 0.05), and chronic obstructive pulmonary disease (COPD) was significantly correlated with RP ≥ grade 1 (X² = 9.146, P < 0.05). However, there was no significant correlation between RP and different irradiation techniques, chemotherapy factors, radiotherapy dose, esophageal cancer stage and cancer location. The result of multivariate analysis showed that V₅ and V₄₀ were independent risk factors of RP ≥ grade 1 (AUC 55.74%, 4.13%), MLD was independent risk factors of RP ≥ grade 2 (AUC 11.91 Gy), and V₅ was independent risk factors of RP ≥ grade 3 (AUC 57.60%). The smoking index > 400 was the independent risk factor of RP ≥ grade 3 (Wald = 5.964, P < 0.05), and COPD was the independent risk factor of RP ≥ 1 grade (Wald = 6.110, P < 0.05). Conclusions: The incidence of RP is low after radiotherapy for thoracic segment esophageal cancer. The dosimetric parameters such as lung V₅, V₄₀, MLD, smoking degree, COPD and other clinical characteristics are closely related to the occurrence of RP of corresponding grades. (authors)