As the critical cytokine in pulmonary fibrosis, radiation-activated TGF-β triggers the EMT in AT2 cells (Figure 2), which increases mesenchymal genes N-cadherin and vimentin, as well as inhibiting epithelial genes ZO-1 and E-cadherin; it also transforms the morphology of epithelial cells into mesenchymal cells to produce a large amount of ECM [27,32]. Here, TGFB1 is linked to pulmonary fibrosis.