Adaptive radiotherapy for preoperative gastric cancer

Preoperative radiotherapy for gastric cancer is a novel treatment approach, aiming to precisely irradiate the target while sparing the surrounding healthy tissue to limit potential adverse side effects. However, the stomach's inherent motion and deformation, as well as its proximity to vital organs, pose challenges for precise irradiation. A promising solution is adaptive radiotherapy, which adjusts the treatment plan to match daily anatomical variations. One such approach is a Library of Plans (LoP), where multiple treatment plans covering various anatomical variations are created, and the most suitable plan is selected daily. This thesis explored a CBCT-guided adaptive strategy for preoperative gastric cancer radiotherapy. The observed substantial stomach motion and deformation highlights the need for an adaptive strategy. The feasibility of a CBCT-guided LoP was demonstrated through observer evaluations, showing that a range of observers can consistently select the most appropriate treatment plan. Furthermore, using a gastric deformation model, stomach shape was predicted from stomach volumes. A dosimetric comparison between the LoP and a single-plan approach showed that the LoP reduces the average irradiated volume and the dose to organs at risk while maintaining equal target coverage. Hence, this research underscores the benefit of an adaptive strategy for preoperative gastric cancer radiotherapy and contributes to understanding the challenges and potential solutions in this field.