Hi Leon.
Mate, how does anyone answer that?
You might have to be selfish and do what is right for you. It wont go down well perhaps, although a 600 km round trip does not go down well either.
Why does your lad not move closer for the duration of treatment? That would be the best idea, particularly if he is off work already.
There is no right or wrong answer here, although my grandfathers words keep ringing in my ears. "Help some one in the smallest way and they will appreciate it the most"
Oh, and yes, I understand the nature of the disease better than most will know.