213 The work presented in this thesis covers a range of topics with a common denominator: magnetic resonance imaging (MRI)-guided radiotherapy for the treatment of prostate cancer. The aims of this thesis were to explore and to evaluate technological and clinical aspects of MRI-guided stereotactic radiotherapy for the treatment of primary localised prostate cancer (part I) and locally recurrent prostate cancer after primary radiotherapy (part II). In this chapter, the presented work will be discussed and put into the broader context of MRI-guided radiotherapy for localised prostate cancer. Furthermore, future perspectives for MRI-guided stereotactic body radiation therapy (SBRT) for the treatment of prostate cancer will be discussed. Part I. MRI-guided stereotactic radiotherapy for primary localised prostate cancer Clinical introduction of MRI-guided radiotherapy for prostate cancer The introduction of new innovations not only demands its (early) adopters to evaluate the suggested benefits and potential downsides, but also pushes them to explore how the new technology could be implemented and used in clinical practice. The adopters need an open mind and creative thinking to be able to cope with the changes that are needed to adopt a new technology. Particularly for MRI-guided radiotherapy using a 1.5 Tesla (T) MR-Linac, the implications of introducing this technology into the clinic have been vast. MRI-guided radiotherapy has led to a redesign of how we approach the treatment of our patients. With conventional radiotherapy treatment, a large part of the work (i.e. treatment preparation) was carried out before the patient was actually treated: imaging, contouring, treatment planning, and approval of the treatment plan. MRI-guided radiotherapy has changed the way we look at this treatment preparation phase as something that is only carried out before the actual treatment. Imaging, contouring, treatment planning, and approval of the treatment plan are performed repeatedly on a daily basis with online adaptive MRI-guided radiotherapy. This requires a different mindset for those who are involved, including radiation oncologists, radiation therapists (RTTs), physicists, and technicians. With conventional radiotherapy, the tasks and responsibilities were well defined. However, with the introduction of online plan adaptation in MRI-guided radiotherapy, tasks and responsibilities had to be re-defined. Early on in this process, the traditional division of tasks was more or less copied from the offline to the online MR-Linac workflow. This meant that radiation oncologist needed to be present during each treatment fraction, in order to delineate the target and to approve the treatment plan. Furthermore, a medical physicist had to be present for plan quality assurance (QA). Given the additional workload for radiation oncologists and physicists during treatment, this was regarded unfeasible if the numbers of patients being treated on an MR-Linac would increase significantly. As suggested by Hales et al.1, an RTT-led workflowwas needed to feasibly integrate MRLinac treatment into radiotherapy departments worldwide. In chapter 2, we discussed a part of this new role for RTTs. In this chapter, we focused on the contouring part of the online workflow, as this serves as the basis for the treatment planning and actual treatment delivery and thus is a crucial step in the workflow. However, the change to an RTT-led workflow entails much more than just the contouring part. Particularly for prostate cancer treatment, RTTs at our department were trained to 11 General discussion and future perspectives
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