Head and Neck Neoplasms/radiotherapy; Lymphocyte Depletion; Radioimmunotherapy/methods; STAT3 Transcription Factor/antagonists & inhibitors; Squamous Cell Carcinoma of Head and Neck/radiotherapy; T-Lymphocytes, Regulatory/radiation effects; Analysis of Variance; Animals; Cytotoxicity, Immunologic; Female; Forkhead Transcription Factors/genetics; Gene Expression Profiling; Head and Neck Neoplasms/genetics; Head and Neck Neoplasms/immunology; Humans; Immunologic Memory; Interleukin-2 Receptor alpha Subunit/genetics; Lymphocyte Depletion/methods; Macrophages/radiation effects; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Nude; Myeloid-Derived Suppressor Cells/radiation effects; Radiation Tolerance; Radiotherapy, Image-Guided; STAT3 Transcription Factor/metabolism; Squamous Cell Carcinoma of Head and Neck/genetics; Squamous Cell Carcinoma of Head and Neck/immunology; T-Lymphocytes, Regulatory/immunology; T-Lymphocytes, Regulatory/metabolism; Transforming Growth Factor beta1/genetics; Tumor Microenvironment