End-to-End (E2E) testing is a method originating from computer science that is designed to determine whether an application communicates as required with hardware, networks, databases, and other applications. This paper is to advocate that the quality management (QM) of modern radiation therapy (RT) would benefit from more regular use of E2E based quality assurance (QA) in the local clinic. The argument is that modern RT delivery is performed through some process linked by a chain of interdependent stages and actions mediated by complex interchanges during the patient’s treatment. These actions along the chain are often modified due to decisions by clinical staff who are interpreting information acquired along the process. While physics QA can validate that each of these steps are technically achievable (e.g., through machine QA) such conventional QA does not guarantee that the overall process is being carried out as planned even when it has been described by a well-defined protocol and delivered by well-trained staff. The paper briefly reviews the changes in programmatic design as RT has become more complex, the associated changes in RT QM, and some past examples of E2E testing in RT clinics, usually performed during the implementation of some new RT technique or during external audits of the clinic’s practice. The paper then makes the case for increased E2E QA based on the lessons learned from this experience and ends with some suggestions for implementing effective and sustainable E2E testing in a clinic’s QM program.