RAI

The docs like to give you plenty of time for your wound to heal before they zap you with the radiation - that's one reason for the gap between surgery and RAI.

The other is that if they want you to do a low iodine diet, you need to be on that for at least a couple of weeks.

And finally, depending on whether thyrogen injections are available, it can take up to 6 weeks to wean you off the medication and prepare you for the RAI (this doesn't happy that often any more, but it is a consideration).

So I would say you're probably OK for the dates with your brother, and if the doc wants you whilst you are out of the country, he'll just have to wait. It's not unusual for RAI to be up to half a year after surgery (and even longer during lockdown) and a delay of a few weeks shouldn't be make a material difference. 

Thank you barbara always answer my questions and my mind peace during this hard time

Family first. The RAI can wait a couple of weeks.