Risk of radiation pneumonitis in patients with emphysema after stereotactic body radiotherapy for non-small cell lung cancer assessed by quantitative CT

Quantitative CT assessment of patients with pulmonary emphysema is used to measure pulmonary function. The present study evaluated whether the quantitative CT value can accurately estimate the risk of radiation pneumonitis (RP) after stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) in patients with and without emphysema. A total of 80 patients with stage I NSCLC receiving SBRT at a dose of 50 or 60 Gy in five fractions at our hospital between November 2003 and October 2015 were included in the analysis. A total of 33 (41%) patients were diagnosed with emphysema on CT examination. Dosimetric parameters, quantitative CT percentage value of low attenuation area (LAA%) in the whole lung, and average whole lung CT density values were used to examine the risk of RP. Among the 80 patients, 26 (33%) and 3 (4%) experienced Grade 1 and Grade 2 RP, respectively, during the median observation period of 18.8 (1.8-106.8) months. The RP rate for patients with a LAA% (<-910 HU) of <= 25% was significantly higher than that of subjects with LAA% (<-910 HU) >25% (P=0.037). The RP rate in subjects with an average HU value of >-790 HU was significantly higher compared with that of patients with <=-790 HU (P=0.036). Age (hazard ratio [HR]=2.46; P=0.03) and average HU (HR=3.39; P=0.02) were significantly associated with RP, whereas mean lung dose was not identified to be significant in multivariate analysis. The quantitative CT value was associated with RP after SBRT.