Potential benefit and clinical implementation of adaptive radiotherapy

The success of radiotherapy is defined by how well we are able to treat the tumor, without overly damaging the healthy tissue. Over the entire treatment period, day-to-day anatomical variations will occur, which can be compensated for by using a different irradiation plan for each treatment day. This is called adaptive radiotherapy. In this thesis, a range of aspects concerning adaptive radiotherapy are addressed using three different applications: radiotherapy for bladder cancer, rectum cancer and esophageal cancer.
For bladder cancer radiotherapy, we showed that efforts to reduce the dose to the healthy tissue reduce the rates of toxicity (chapter 2). By implementing an adaptive strategy, not only the bowel cavity dose reduces, but target volume irradiation improves as well (chapter 3). In chapter 4, we compared our strategy with the strategy of another institute, to find which strategy is favorable.
For rectal cancer radiotherapy, we designed an adaptive strategy that results in a small improvement in target volume irradiation. For individual patients, substantial reductions in healthy tissue irradiation were found (chapter 5 and 6).
For esophageal cancer radiotherapy, we found a significant cardiac volume reduction over the course of treatment (chapter 7), but this did not warrant an adaptive strategy (chapter 8).
Overall we showed that for individual patients, the benefit of an adaptive strategy can be substantial. However, the increase in workload associated with adaptive radiotherapy warrants careful patient selection. The clinical value of adaptive radiotherapy remains unknown until prospective studies have shown actual improved patient outcomes.