For example, only a human doctor can make a "diagnosis" or write a prescription. Even just making "treatment recommendations" (e.g., a more-effective treatment or one with less side effects than the current one), which would then be reviewed and approved by an appropriately-licensed physician, is a problem.
Not having worked in the radiology space, my naive hunch is that it has to be framed as a "screening tool" which "helps the physicians find cancers." (Which can be justified to regulators because ML tends to have higher recall than humans on these tasks, albeit lower precision).
In theory, ML helps doctors spot cancers they wouldn't ordinarily see. In practice, it probably means that the physicians still technically "review" all images, but only give a cursory glance to those not flagged by the system.
I know I read press releases ages ago saying "hey look, we can do this machine learning", but I haven't really heard anything about it since.