PET in Oncology
It's much more complex. Radiopharmaceutical tracers are produced in different ways and have different half lives. FDG has a relatively long half life and can be transported, other tracers have very short half lifes and so must be produced onsite. They have different mechanisms of action and so are used for different purposes and have very different costs of production. There is a wide literature on this topic - just search for tracers and PET.