BACKGROUND: For lung cancer patients with poor pulmonary function due to emphysema or fibrosis, it is important to predict the amplitude of internal tumor motion to minimize the irradiation of the functioning lung tissue before receiving stereotactic body radiotherapy. MATERIALS AND METHODS: Two board-certified diagnostic radiologists independently assessed the degree of pulmonary emphysema and fibrosis on computed tomography (CT) in 71 patients with peripheral lung tumors before real-time tumor-tracking radiotherapy (RTRT). The relationships between CT findings of the lung parenchyma and the motion of the fiducial marker near the lung tumor were investigated. Thirty patients had normal pulmonary function. Twenty-nine patients had obstructive pulmonary dysfunction (FEV1/FVC < 70%), 6 patients had constrictive dysfunction (%VC < 80%), and 16 had mixed dysfunction. RESULTS: The upper region was associated with smaller tumor motion, as expected (p=0.0004), and presence of fibrosis (p=0.088) and pleural contact of the tumor (p=0.086) were weakly associated with the tumor motion. The presence of fibrotic change in lung tissue was associated with smaller tumor motion in the upper region (p<0.05) but not in the lower region. The findings of emphysema and pulmonary function tests were not associated with tumor motion. CONCLUSIONS: Tumors in the upper region of lungs with fibrotic changes have smaller motion than those in the upper region of lungs without fibrotic changes. Tumor motion in the lower lung region was not significantly different between patients with and those without lung fibrosis. Emphysema was not associated with the amplitude of tumor motion.