The machine in the airport only scans things inside it, it doesn’t leak X-rays outside. In hospital the entire room with the patient is the machine. The reason for this is that it’s not possible to remove a part of a human body, put it in the scanner and then put it back on the body. And full body X-rays would be excessive and unnecessarily dangerous. So they only shoot X-rays through the specific body part in interest while the patient is in the room.