External beam radiation therapy (known as radiation therapy) is a local cancer treatment that uses high radiation dose to damage the deoxyribonucleic acid (DNA) of cancer cells with specific part of patient body. A linear accelerator (linac) customizes high energy x-rays or electrons to conform to a tumor’s shape and destroy cancer cells while sparing surrounding normal tissue. Beam’s eye view (BEV) imaging technique is used for quality assurance (QA) and treatment planning of radiation therapy to ensure the relative orientation of patient and beam delivery of linear accelerator (linac) machine. The common x-ray image device for linac includes Megavoltage (MV) electronic portal imaging device (EPID) and Kilovoltage (kV) cone-beam CT (CBCT) imaging devices. These devices were initially designed for patient localization purpose. However, the use of EPID and CBCT has been applied for other clinical aspects; such as linac QA, pre-treatment patient-specific QA, motion tracking, and real-time patient verification. In this talk, an introduction of BEV technique as well as the advantage and disadvantage between EPID and CBCT devices will be summarized. Overview of the novel applications that use the BEV imaging technique for clinical use will be presented. It also covers from a real-time data collection using frame grabber card and external workstation connected to linac machine, real-time marker and markerless tumour tracking, patient-specific EPID-based QA, comprehensive VMAT QA, remote auditing, intra and inter-fraction patient treatment verification, and clinically significant anatomical change in cancer patient during treatment course.