Purpose: To determine changes in pulmonary function brought about by lung stereotactic body radiation therapy (SBRT).
Methods: One hundred and twenty-seven patients were treated with lung SBRT using 48 to 60Gy in four to five fractions on a prospective trial. We obtained pulmonary function tests (PFTs) at baseline, 6 weeks, 3 months, 6 months, 9 months, 12 months, and 24 months after SBRT. Group mean PFT parameter values are reported.
Results: At baseline forced expiratory volume in 1 second (FEV1) was 1.5 l (67% predicted, range: 0.4-3.4 l), corrected diffusing capacity for carbon monoxide was 12.2 ml/min/mmHg (50.8% predicted, range: 3.3-27.2 ml/min/mmHg), and total lung capacity was 5.7 l (102.4% predicted, range: 3.1-9.1 l). At 12 months, there was decline in FEV1 (-4.1%; p = 0.01), corrected diffusing capacity for carbon monoxide (-5.2%; p = 0.027), forced vital capacity (-5.7%; p = 0.004), and total lung capacity (-3.6%; p = 0.039). Declines in FEV1 (-7.6%; p = 0.001) and forced vital capacity (-8.9%; p = 0.001) persisted at 24 months. Rates of pneumonitis were 3.1% and 0.8% for grades 2 and 3, respectively. There were no grade 3 PFT toxicities at 12 months. Lower PFTs at baseline and 1 year after SBRT did not predict for worse overall survival.
Conclusions: As the largest cohort of patients with prospective follow-up PFT evaluation after lung SBRT, this supports the safety of SBRT in this population of predominantly medically inoperable patients. While statistically significant, nearly all declines in PFTs would be rated as a grade 1 on the Radiation Therapy Oncology Group scale, demonstrating safety. PFT declines were not associated with worse overall survival.