CD8A and breast cancer: This study intends to detect the levels of peripheral blood lymphocyte subsets (CD3 + T cells, CD3+/CD4 + T cells, CD3+/CD8 + T cells, CD4+/CD8 + ratio, natural killer (NK) cells, and B cells) in breast cancer patients before RT to understand the immune function of patients and investigate the impact of immune status on the severity of ARD.