Timing and characteristics of radiation pneumonitis after stereotactic body radiotherapy for peripherally located stage I lung cancer

Background This study was conducted to determine the timing and characteristics of radiation pneumonitis (RP) associated with stereotactic body radiotherapy (SBRT) for stage I lung cancer. Methods Two hundred thirty-one patients treated with SBRT using 52 Gy in 4 fractions were identified. Control rate, RP incidence rate, and predictive factors and timing of RP were evaluated retrospectively. Results The 3-year overall survival and local control rates were 80.7 and 92.0 %, respectively. The grade >= 2 RP rate was 13.0 %; no grade 4-5 RP occurred. The most statistically significant predictive factor of grade >= 2 RP was V10. The median intervals to first graphical appearance were 4.2 and 2.5 months for grade 1 and grade 2-3 RP, respectively. Median intervals to maximum radiological density change were 6.0 and 4.6 months for grade 1 and grade 2-3 RP, respectively. A significantly different interval to first graphical appearance between grade 1 and grade 2-3 RP was observed; no significantly different interval to maximum radiological density change was noted. Conclusion The first graphical appearance of grade >= 2 RP was earlier than that of grade 1 RP, although the timing of maximum radiological density change was not significantly different.