First, according to our proposed model, if patients are at high risk of G4 lymphopenia, measures can be taken before treatment, such as correcting anemia, modifying EBRT plan to reduce PTV_5500 Dmax, or restoring a physiological number of lymphocytes in the peripheral blood by use of cytokines IL-2, IL-7, and IL-15, which play a role in the development, proliferation, and survival of T cells (18). Here, IL2 is linked to lymphopenia.