Hi Katherine!!!
We have had several cats with thyroid(hyper)disease. Boo was the first. We had the radioactive method done on Boo. She was doing well, when SUDDENLY, one morning I looked at her and thought she was dying. She was rushed to the vet. Blood work was done. The vet threw in a T4. Despite the last time Boo's T4 were was checked, and it was NORMAL, this T4 showed Boo had NO circulating thyroid hormone at all in her system. It was a life threatening situation. Once stablized, Boo had to get a daily dose of Solixine until the day she went to the Bridge.
Another thyroid kitty, was little Molly Meu. Molly was given the transdermal Tapazole. It was very effective for Molly and her T4's were in the NORMAL range.
And now we have Norton. He is 17 yrs old. Norton get the Tapazole pill twice a day. His dose has been successfully titrated to a 1/4 tablet in the morning and a 1/8 of a tablet in the evening. His T4's have been in the normal range.
I have tried all the methods, and to be honest with you, I do not think I would use the radioactive method again. But, perhaps a second opinion is to be considered. Good luck with your kitty!!! Sandra