jra40 - I had a PET scan after my ommaya port was placed and it showed that I have cancer nowhere in my body but my cerebellum. It can help with some aspects of diagnosis, and it is more sensitive in some ways than other imaging modalities but they are all very different is my understanding. Someone in my chemo group's father sold these machines for a living and she felt that in some instances, based on understanding the technologies through him, that PET was better than MRI with contrast.
That said, a whole brain MRI with gadolinium contrast is the standard to look for brain mets. I had one last week. The newer technology is PET-MRI that has been around a few years. That will let them do a metabolic sampling through the imaging to show different energy and nutrient usage in areas where there is supposed disease against where there is not. It was crazy to see how different my LM area was from the unaffected area on that view.
I just got back from talking with an MO and she agreed that if there is nodal involvement in a HER2+ patient that they have to get brain scans yearly -- so some cancer centers do get this. I told her that HER2 patients all over the country, and probably the world, are fighting with their docs to get scans and it is wrong.