I really feel for you. I haven’t had this reaction and it’s a good job too as my lifelong phobia has been for vomiting in any way, shape or form. I’m sure if you raised the matter with your oncologist, they’d sort it out, either with a stronger anti-emetic (I always take cyclizine before I go) or an alternative kind of contrast - you can’t be the first with this kind of reaction and it shouldn’t continue.
I do hope you get it resolved. These are quarterly, with possible additional MRIs , so you can’t put up with this. Take care xx