As shown in Fig. 6e, the TGF-β expression in interstitial brachytherapy group reached its peak with the increase of time from week 1 to week 16, and it was significantly lower than SBRT group (P < 0.05), indicating the presence of more fibrosis-promoting cytokines and heavier pulmonary fibrosis in rats of SBRT group. This evidence concerns the gene TGFB1 and pulmonary fibrosis.