My father in law does this, in a developing country no less. Bless his soul, he's a very kind man. But it's incredibly taxing. Not just the treatments but there are many cases where children die and there's nothing you can do about it. And it doesn't stop, even when he's on vacation, he has patient's families calling/texting him.

I've been at dinner where someone will walk over and say something like "you saved my brother/daughter/sister/son's life." Or sometimes my wife and I will meet someone who will recognize she's his daughter and day the same. Hopefully that makes it worth it.