If you have knowledge both in biology as a physician and can code, you can also become a bioinformatician, where you can still apply ML. Maybe the difference will be that it will be more on the application side of the ML rather than the theoretical part.

Also, I will be cautious about "... landing a PhD position at a good US school", from my experience and others, I've found out that it's more important to look after a supervisor with whom you can resonate rather than chasing a reputable institution.

(Disclaimer, I'm a PhD student in the UK)