Predictors of pneumonitis-free survival following lung stereotactic body radiation therapy

Sibo Tian, Jeffrey M. Switchenko, Richard J. Cassidy, Chase E. Escott, Richard Castillo, Pretesh R. Patel, Walter J. Curran, Kristin A. Higgins


Background: Radiation pneumonitis is a common toxicity following lung stereotactic body radiation therapy (SBRT). We explored whether motion management technique, in conjunction with patient and treatment characteristics, is a predictor of radiation pneumonitis-free survival (PNFS).
Methods: A single institution multi-center lung SBRT database was retrospectively reviewed. PNFS was defined as time to earliest onset of radiation pneumonitis or last clinical follow-up. Patients were simulated using a 4-dimensional approach, and those with 1 cm or greater tumor motion were selected for respiratory-gated treatment. Real-time Position Management and phase-based gating were employed. Univariate and multivariable Cox proportional hazard models were fit for relevant covariates to determine the impact of free-breathing versus respiratory-gated treatment on PNFS.
Results: The initial treatment courses of 208 patients were included, with a median follow-up length of 23 months. The median age at treatment was 71 years. About 91.8% of patient had early stage (T1–2) non-small cell lung cancer and were treated with common regimens including 10 Gy ×5, 12 Gy ×4 and 18 Gy ×3; 26.4% underwent respiratory-gated SBRT. The overall rate of grade 3 or higher radiation pneumonitis was 10.1%. PNFS was not significantly different between patients treated with respiratory-gated versus free-breathing SBRT (HR =0.88; P=0.707); tumor location and fractionation were predictors of PNFS in the multivariate setting.
Conclusions: The method of motion management does not appear to impact PNFS when the tolerance for tumor displacement is 1 cm or less for free-breathing treatment planning and delivery. This approach may be appropriate when selecting patients for respiratory gating.