Adjuvant radiotherapy in node-negative salivary malignancies of the parotid gland: A multi-institutional analysis

•Adjuvant radiotherapy improved locoregional control and survival for node-negative high grade parotid gland cancer.•Radiotherapy is recommended for low grade parotid gland cancer with advanced T stage or involved resection margins.•Histologic grade is an independent prognostic factor for node-negative parotid gland cancer.•Higher biologic effective dose (≥77 Gy10) is associated with increased disease control.