The phantom was based on the 4D extended cardiac-torso (XCAT) phantoms, developed by the Duke University. These models provide high resolution segmented anatomical data sets, based on segmentations of patients and the Visible Male and Female anatomical datasets from the National Library of Medicine (19 (link)). The volume of the organ models that can be generated using these phantoms are representative of 50th percentile males and females, based on height and weight (20 (link)) For the creation of our phantom we chose the female model because of the peritoneal extension in the pouch of Douglas, resulting in a more complex model. The organ models were imported as delineations into 3D slicer (21 (link), 22 ) to create a peritoneal surface. HIPEC treatments can be performed with an opened or closed abdomen, each with their respective (dis)advantages. For this study we chose to design a phantom based on an open HIPEC treatment, since larger thermal gradients are expected during open HIPEC treatments compared to closed HIPEC treatments, which will thus be a better test for the model performance. All surfaces were imported into the 3D modelling and rendering package Blender (23 ) to create a 3D-printable model, see Figure 1A. The model was printed in two different parts using a Fortus 450mc 3D-printer (Stratasys). Walls consisted of 4 layers of acrylonitrile styrene acrylate (ASA) red (Stratasys), all 0.508 mm thick. After printing, the two parts were connected using mortise and tenon connections. The outside of the model was covered with a PVC coating to make the phantom waterproof. Organs and peritoneal exterior were not coated to allow water to seep in, filling the organs with water. This was done to mimic tissues and generate a realistic thermal conductivity. It took about one day to fill the organs and peritoneal exterior with water and therefore, the phantom set-up was stabilized at the start of the experiments and no additional water was seeping into the organs during experiments. An additional effect was the thermal interaction between the relatively cold organs and relatively warm peritoneal cavity which also occurs during HIPEC treatments. The 3D-printed phantom is shown in Figure 1B.
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