The technique for determining the exact area to be radiated after certain forms of breast cancer surgery is relatively imprecise. This research focuses on being able to locate this area more precisely. During breast cancer surgery, after removing the tumor, we applied hydrogel in the empty space that the tumor left behind. After surgery, this hydrogel is visible on CT scans. Therefore, the area to be radiated can be more precisely located. Hence, less healthy tissue will be unnecessarily affected by radiation.