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Dear Dr. Roach: I'm a 74-year-old male who is in good health and works out. I recently had a thyroidectomy for thyroid cancer and had my entire thyroid removed. This month, I'm scheduled for a radioactive thyroid treatment. I understand this should cleanse any remaining cancer that was left around this area. I was told to drink plenty of fluids so that I can drain my bladder every 1.5 hours, so as not to damage my bladder.
My question is: How is this affecting the rest of my body? If it can negatively affect my bladder, what about my organs and, in particular, my heart and stomach? I take 24-hour Nexium twice a day for acid reflux. Should I cancel the treatment or be worried about it? -- J.P.
Answer: I hope that I can help your excess worry because I certainly don't think you should cancel the procedure. Iodine is a chemical element that's required for making thyroid hormone. (Chemically, it's called triiodothyronine, which emphasizes the necessary iodine within its chemical structure.) Iodine that's absorbed by the body is actively taken up by thyroid hormone-producing cells, which are found in the normal thyroid tissue for most people.
However, iodine also gets taken up by most thyroid cancer cells, whether they are still in the neck or have spread elsewhere. The radioactive isotope (I-131) kills cells that are within about 0.6 mm, so it precisely targets thyroid-producing cells. Because iodine gets taken up avidly by thyroid cells, the danger to your stomach and heart is minimal, as radioactive iodine passes through them very quickly.
I-131 reaches concentrations in the thyroid tissue that are 50 times higher than those in the blood. But when it's released, it's excreted through the bladder, which is why you want to "flush out" the bladder with water.
They're waiting at least four weeks (ideally 6-12 weeks) between surgery and the radiation treatment so that the thyroid cells will be very deficient. (You aren't being given thyroid hormone now, so any residual thyroid cells and thyroid cancer cells will be working hard to make the hormone. In the process, they'll take up I-131, which will kill them and their neighbors.)
I say "most" thyroid cancer cells take up iodine because some types of thyroid cancers have mutations that prevent them from taking up iodine, in which case radioactive iodine fails. Fortunately, this isn't the case with most thyroid cancer cases, which have a very high cure rate with combination treatment.