Stereotactic body radiotherapy for lung cancer in patients with interstitial lung disease

Stereotactic body radiotherapy (SBRT) is a highly dose-concentrated radiotherapy that can spare damage to normal organs much more than conventional radiotherapy. Severe radiation pneumonitis (RP) after stereotactic SBRT for thoracic lesions is rare but sometimes gets severe. In this review, we presented the reported frequency of severe RP after SBRT for stage I NSCLC, its risk factors, and the attempts at clarifying individual predictive risk factors. The ratio of fatal RP after SBRT for lung tumor in patients with accompanying pulmonary interstitial changes is more than 5%, and overall survival is poor. The dose to the normal lung and interstitial changes in the background lung are important predictive factors of severe RP, with idiopathic pulmonary fibrosis (IPF) being the biggest risk factor for severe RP, but these interstitial lung diseases (ILDs) are not always a contraindication for thoracic SBRT. Based on the high fatality rate, it would be reasonable to avoid prompt SBRT by watchful waiting in cases of indolent or non-aggressive tumors, such as ground-glass tumors. It would be better to use or recommend more highly precise irradiation systems or particle therapy (PT) that can reduce radiation doses to the normal lung more, in particular for the cases with IPF. Identification of biomarkers indicating an individual’s risk level for severe RP, such as single nucleotide polymorphisms (SNPs), would be important in treatment decisions, but it needs further research. Though there are no reliable drugs for treating severe RP, anti-fibrotic agents, such as pirfenidone, might be effective in its prevention or alleviation.