John Lithgow
John Lithgow was something of a De Palma regular and I wonder if he was considered for the role of Dr, Elliott? It’s hard to imagine him not being terrific in the part - which is not a knock on Michael Caine, who is impeccable.
Lithgow was of course a familiar face but very much a character actor. Perhaps De Palma wanted a big name in this striking role, and Caine was certainly a star at the time.