[18F]F-FAPI PET/CT and Laparoscopy in Staging Advanced Gastric Cancer

The goal of this clinical trial is to learn if a new type of scan, FAPI-PET/CT, can help find metastases of gastric cancer. We want to know how well this scan works for this purpose and whether it is less burdensome for patients compared to the methods we currently use to find metastases. The main questions it aims to answer are: * In how many patients can FAPI-PET/CT find metastases, which leads to a change in their treatment plan as decided by their medical team, such as avoiding unnecessary surgeries and changing from treatment meant to cure the disease to treatment focused on comfort (palliative treatment)? * In how many patients does FAPI-PET/CT change the diagnostic process as decided by their medical team, like more biopsies or imaging, or changing the type (extent) of surgery needed? Apart from the usual care gastric cancer patients receive, participants will: * Undergo one additional scan, which will take approximately 2 hours in total (excluding travel time) * Complete a number of questionnaires, which will take approximately 4 hours in total