TGFB1 and radiation pneumonitis: While most of the experimental data that provide proof for the role of TGF-β1 in radiation fibrosis are obtained from in vitro studies or from animal models that correlate TGF-β1 expression with normal tissue radiation injury [14], [26]–[28], some previous studies have addressed the role of TGF-β in radiation injury by inhibiting its expression or its signaling [29]–[32].