I've heard of that treatment too. We didn't do it for our Genevieve, because it necessitated 4 to 6 weeks in isolation and she also was suffering from intestinal cancer and was under chemo by pill to make her more comfortable. Not knowing how much time she would have left because of the cancer, I couldn't stand being separated from her that long. But I have heard of the excellent results radiation therapy has achieved with hyperthyroid cats. Welcome to Pet Talk!