Whole brain radiotherapy (WBRT) has long been a practical and effective therapeutic modality for various settings of management in radiation oncology. For example, the indications for WBRT should include brain metastasis or metastases, the setting of prophylactic cranial irradiation (PCI) used mainly for patients with limited-stage small cell lung cancer, and even some patients with extensive-stage small cell lung cancer. The rationales for WBRT are essentially based on that it can target both microscopic and gross intracranial disease.