Background: To assess for variables predicting pulmonary function test (PFT) changes after stereotactic body radiotherapy (SBRT) for medically inoperable stage I lung cancer.
Methods: We reviewed 92 consecutive patients undergoing SBRT for stage I lung cancer between February 2004 and August 2007. A total of 102 lesions were treated using prescriptions of 20 Gy x 3 (n = 40), 10 Gy x 5 (n = 56), and 5 Gy x 10 (n = 6). Institutional practice was 10 Gy x 5 before March 1, 2006 before changing to 20 Gy x 3 to conform to RTOG 0236 unless otherwise dictated clinically.
Results: Median pretreatment forced expiratory volume at 1 second (FEV1) was 1.21 liter (50% of predicted) and median diffusion capacity to carbon monoxide (DLCO) was 56.5. There was no significant overall change in PFT's after SBRT. Individual patients experienced both substantial improvements and declines (10% declined at least 14% predicted FEV1% and 19% predicted DLCO). The mean change in FEV1 was -0.05 liter (range, -0.98 to +1.29 liter; p = 0.22) representing -1.88% predicted baseline FEV1 (range, -33 to + 43%; p = 0.62). DLCO declined 2.59% of predicted (range, -37 to +33%; p = 0.27). Conformality index, V5 and V10 were associated with individual patient changes in FEV1% (p = 0.033, p = 0.0036, p = 0.025, respectively), however, correlations were small and overall treatment dose did not predict for changes (p = 0.95). There was no significant difference in FEV1 (p = 0.55) or FEV1% (p = 0.37) changes for central versus peripheral locations. No factors predicted for individual changes in DLCO. Patients with FEV1% below the median of the study population had significantly longer overall survival (p = 0.0065). Although patients dying of cardiac disease died earlier than those dying of other causes, FEV1% below median was not associated with a lower risk of dying of cardiac disease or with lower Charlson comorbidity index.
Conclusions: (1) SBRT was well tolerated and PFT changes were minimal. (2) Central lesions were safely treated with 50 Gy.