Retrospective Cohort Study of Bronchial Doses and Radiation-Induced Atelectasis After Stereotactic Body Radiation Therapy of Lung Tumors Located Close to the Bronchial Tree

Purpose To evaluate the dose–response relationship between radiation-induced atelectasis after stereotactic body radiation therapy (SBRT) and bronchial dose. Methods and Materials Seventy-four patients treated with SBRT for tumors close to main, lobar, or segmental bronchi were selected. The association between incidence of atelectasis and bronchial dose parameters (maximum point-dose and minimum dose to the high-dose bronchial volume [ranging from 0.1 cm3 up to 2.0 cm3 ]) was statistically evaluated with survival analysis models. Results Prescribed doses varied between 4 and 20 Gy per fraction in 2-5 fractions. Eighteen patients (24.3%) developed atelectasis considered to be radiation-induced. Statistical analysis showed a significant correlation between the incidence of radiation-induced atelectasis and minimum dose to the high-dose bronchial volumes, of which 0.1 cm3 (D0.1cm3 ) was used for further analysis. The median value of D0.1cm3 (α/β = 3 Gy) was EQD2,LQ = 147 Gy3 (range, 20-293 Gy3 ). For patients who developed atelectasis the median value was EQD2,LQ = 210 Gy3 , and for patients who did not develop atelectasis, EQD2,LQ = 105 Gy3 . Median time from treatment to development of atelectasis was 8.0 months (range, 1.1-30.1 months). Conclusion In this retrospective study a significant dose–response relationship between the incidence of atelectasis and the dose to the high-dose volume of the bronchi is shown.