I'm at the tail end of my 10 year passport validity, and I had a bit more hair 10 years ago than I do now (male pattern balding). Started routinely shaving my head 4-5 years ago. Only place that has ever commented on my hair change was entry immigration in Cambodia, where the agent processing my arrival visa remarked how the guy in the picture was doing better than the person standing in front of him. I would not be concerned at all.

Best wishes with your treatment.