What to expect from a radioactive treatment...?

my son is 10 and he got papailary cancer on tyroid hes been trough 2 major surgery and now his on a diet of low iodine and in a month his getting radioacticve im realy scared cause they took him of his tyroid medicine for this period of time and that has me worry but its part of this treatment if any one out there is going through this and has info more that can share with me i would apreciate thank you and god bless everyone