To this end, this study observed the serum levels of serum MMP-9 and SAA in patients with sCAP caused by radiotherapy for esophageal cancer, explored their diagnostic value in pneumonia, and analyzed the effects of the two and the physical factors of radiotherapy on the occurrence of sCAP, with a view to clinical practice providing reference for correct diagnosis and evaluation of RP and sCAP. The gene discussed is MMP9; the disease is pneumonia.