ESTRO 2020 Abstract book

S439 ESTRO 2020

OC-0708 Development of an anthropomorphic multimodal abdominal 4D Phantom for MR-guided Radiotherapy A. Weidner 1,2 , T. Buening 1,3 , A. Runz 1,4 , G. Echner 1,4 1 German Cancer Research Center DKFZ, Medical Physics in Radiation Oncology, Heidelberg, Germany ; 2 University of Heidelberg, Faculty of Medicine, Heidelberg, Germany ; 3 Mannheim University of Applied Sciences, Faculty of Informationtechnology, Mannheim, Germany ; 4 Heidelberg Institute for Radiation Oncology HIRO, National Center for Radiation Research in Oncology NCRO, Heidelberg, Germany Purpose or Objective The anthropomorphic abdominal 4D phantom will serve to further develop and assure the quality of new irradiation techniques, such as MR-guided Radiotherapy with a MRIdian-Linac. An anthropomorphic displacement of the abdominal organs induced by the diaphragm can be detected and evaluated with the MRI. Material and Methods The Phantom consists of a housing with a lid, which has locked recesses to accommodate three actuators. Furthermore, the Phantom has a modular design, so that it is possible to attach a flexible diaphragm as well as a flexible abdominal wall with different silicones (Fig.1). The actuators can exert pressure on the diaphragm via an exact independent depth adjustment. The housing of the phantom was designed with the CAD software, as well as the silicone moulds for the diaphragm and abdominal wall. The 3D design data was then produced using the Stratasys Connex3 3D printer. Furthermore six eyelets are used inside the case to attach the organ model, so that the organ model can be attached free-floating via 1mm thin elastic cords. With all components and the organ model inside the housing, it was filled with 0.3% respectively 0.7% agarose to achieve soft tissue conditions and contrast for MRI imaging. All experiments were performed at the MRIdian MRI-Guided Linac of the University Hospital Heidelberg

could be achieved, 6.8mm in the cranio-caudal (literature 11.56mm) direction and 6.3mm (literature 3.49mm) in the anterior-posterior direction. The movement ranges of the diaphragmatic, the cranio-caudal and anterior-posterior of a tumor, were compared and can be seen in Figure 2 (b).

Conclusion With the developed phantom and organ model, an organ shift induced by the diaphragm could be detected. Furthermore, the displacement of the organ model is within the range of human capabilities. In addition, the displacement in the cranio-caudal direction should be further strengthened, this could be achieved by loosely attaching the organ model in cranio-caudal direction and by integrating a flexible element on the lower side of the phantom to allow a larger longitudinal movement.

Proffered Papers: Proffered papers 38: Current status of MR guided RT

OC-0709 How to be efficient with online adaptation on a MR-linac T. Janssen 1 , A. Betgen 1 , L. Wiersema 1 , R. Verhage 1 , E. Van der Bijl 1 , F. Pos 1 , M. Donker 1 , P. Remeijer 1 , M. Nowee 1 , U.A. Van der Heide 1 1 Netherlands Cancer Institute, Radiotherapy, Amsterdam, The Netherlands Purpose or Objective Online plan adaptation is slowly becoming clinical practice on dedicated hardware. In a typical workflow, a radiation oncologist (RO) is present to re-contour the target and a new plan will be optimized and delivered. Quality Assurance (QA) needs to be performed online, requiring the presence of a medical physicist (MP). Therefore, online adaptation is a burden on efficiency, logistics and cost. However, full online adaptation may not be necessary for each fraction, allowing for a simpler treatment with no RO or MP required. Thus for online adaptation to become

Results In total, the same experiment was performed at least twice for each version of the phantom in order to ensure reproducibility of the movement and thus induced change in the position of the organ model. The evaluation of the examination for reproducibility resulted in a deviation of 0.7mm, therefore reproducibility can be assumed. The varied each time in 10mm steps. (0mm, 10mm, 20mm and 30mm). Furthermore, the evaluation showed that variant 2 of the phantom approximates to the range of motion of a human being (Figure 2). With version 2 of the Phantom, the movement ranges closest to the human area