I did something similar and also got a laugh. We isolated Surfeit for a couple of days, just in case anyone was checking the garbage with a Geiger counter. (Come to think of it, I don't remember what we did with that litter box). Then he got to be with us and the other cats. He hated being isolated. His T4 was perfect several months after the treatment. He also didn't tolerate methimazole, his liver was being damaged by it, so there really wasn't a choice in his case.sent the scary handout they gave us to my best friend who is an environmental engineer in our state. She had a really good laugh about it.
It's not true that you can't destroy normal thyroid tissue with I-131. We know that because it happened after atomic bomb explosions and after the accident at Chernobyl. But the dose of I-131 given is based on the estimated size of the abnormal thyroid adenoma tissue (calculated from the thyroid hormone levels) and is usually pretty accurate. As mentioned above, the rare patient needs to be re-treated and an even rarer patient ends up with thyroid insufficiency and needs to receive thyroid supplements. But, as Antonio65 mentioned, thyroid supplements do not cause the complications associated with methimazole, so they are less objectionable.