when it was in the theaters and won the Golden Globe for Mr Blatty--and was nominated for 2 other Globes--it was called Twinkle Twinkle Killer Kane--it is now The Ninth Configuration----WHY----
I believe that it was kind of obscure for wide release. The ninth configuration is, allegedly, some kind of theorum for proving the existence of God or a higher being. I think that Warner was marketing it as a supernatural thriller and The Ninth Configuration sounds kind of ominous.
This film is an adaptation of Blatty's 1978 novel, The Ninth Configuration, which was itself a rewrite of his Twinkle, Twinkle, "Killer" Kane, from 1966. Blatty was never satisfied with TTKK, but considered his reworking of it into Ninth Configuration his best work at that time.
I think the reason could be that the name gives too much about the movie & the central character.
IMO they wouldn't want us to suspect that the doctor is a patient at the outset. Sure, they do reveal it much before the ending but still. I could be wrong though.
This is your life and it's ending one minute at a time.