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.
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 (¦Á/¦Â = 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).
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.