My cousin's son had a port for vincristine and everything went very well. He did not have a hemangioma though he had KHE which is different and I believe he finished the treatment around 1 year of age and is still being monitored now (he is almost 3)
Did your son have any treatment before 6 months ago? Or did he just start treatment then? I guess Im just wondering because you mentioned his birthmark is pretty big and on his head and neck. I was just wondering because as far as I know (and I'm NOT an expert) I thought that hemangiomas grow for about a year (generally speaking) and then start to involute slowly at that point and it just seems a little unusual to me that his hemangioma would still be growing even though it is being treated and he is 21 months old. Maybe some other people will have more insight into this and they will chime in. Sometimes more complicated "hemangiomas" are difficult to diagnose....not that I'm saying that's true for your son, but I guess I was just curious what he has had for treatment and where he was going, etc.
Anyways, I wish you the best of luck. Like I said, although it was nerve-wracking for my cousin, her son did well with the port and the medicine. I hope everything works out well for you! Keep us posted!