AAPM TG report 330: EPID-based quality assurance of linear accelerators

Electronic portal imaging devices (EPIDs) have been in widespread clinical use for almost two decades due to favorable measurement characteristics such as fast image acquisition, high sensitivity and resolution, digital data format, long-term stability, linear dose response, and large detection area. On-board EPIDs are widely used as a quality assurance (QA) tool to monitor nearly every aspect of linear accelerator (linac) performance. In both the commercial QA equipment market and in clinical practice, there is a trend toward replacing conventional QA approaches with fully automated, EPID-based QA tools. Despite widespread use, EPIDs are complex devices, and there has yet to be consensus or formal recommendations published by the AAPM for their use in routine linac QA. Task Group 330 (TG-330) was, therefore, formed to provide guidelines and recommendations for physicists on the safe and appropriate use of EPIDs for linac QA. In particular, the report: (a) provides a comprehensive review of the characteristics and limitations of EPIDs as time-resolved measurement devices and dosimeters; (b) summarizes the application of EPIDs for linac QA; (c) provides recommendations on efficient and effective implementations of EPID-based QA techniques; (d) describes risks associated with the use of EPIDs for linac QA and provides examples of how risk analysis can be used to ensure the safe use of EPIDs for linac QA. Many of the guidelines in this report are drawn from the literature that is included in the references and from the collective experience of the task group members. This report does not provide recommendations on the implementation of EPID-based patient-specific IMRT or VMAT QA, which is the topic of AAPM's report from AAPM TG-307.