Differences in pulmonary function before vs. 1 year after hypofractionated stereotactic radiotherapy for small peripheral lung tumors

Purpose: To evaluate long-term pulmonary toxicity of stereotactic radiotherapy (SRT) by pulmonary function tests (PFTs) performed before and after SRT for small peripheral lung tumors. Methods and Materials: A total of 17 lesions in 15 patients with small peripheral lung tumors, who underwent SRT between February 2000 and April 2003, were included in this study. Twelve patients had primary lung cancer, and 3 patients had metastatic lung cancer. Primary lung cancer was T1-2N0M0 in all cases. Smoking history was assessed by the Brinkman index (number of cigarettes smoked per day multiplied by number of years of smoking). Prescribed radiation doses at the 80% isodose line were 40-60 Gy in 5-8 fractions. PFTs were performed immediately before SRT and 1 year after SRT. Test parameters included total lung capacity (TLC), vital capacity (VC), forced expiratory volume in 1 s (FEV1.0), and diffusing capacity of lung for carbon monoxide (DLCO). PFT changes were evaluated in relation to patient- and treatment-related factors, including age, the Brinkman index, internal target volume, the percentages of lung volume irradiated with >15, 20, 25, and 30 Gy (V15, V20, V25, and V30, respectively), and mean lung dose. Results: There were no significant changes in TLC, VC, or FEV1.0 before vs. after SRT. The mean percent change from baseline in DLCO was significantly increased by 128.2%. Univariate and multivariate analyses revealed a correlation between DLCO and the Brinkman index. Conclusions: One year after SRT as compared with before SRT, there were no declines in TLC, VC, and FEV1.0. DLCO improved in patients who had been heavy smokers before SRT, suggesting a correlation between DLCO and smoking cessation. SRT seems to be tolerable in view of long-term lung function.