This is because the surgeon has to be careful not to damage your vocal cord nerve and parathyroid glands, which lie close to the thyroid. As the thyroid is the only tissue in the body that takes up and holds onto iodine, a procedure called ablation (ablative radioiodine therapy) is performed to find and destroy any remains of tissue or tumour cells. This involves being administered with radioactive iodine (RAI), which destroys the remaining thyroid gland cells. This is an option for most patients with papillary or follicular types of thyroid cancer.
RAI is given as either a liquid or tablet and you will be encouraged to drink fluids to help the radioiodine pass quickly through your body. Your hospital may require you to stay overnight for 1 to 3 days in a special isolation ward. Talk with your doctor about ways to limit radiation exposure to other people, including children, who may be around you during this time.
It is important to discuss the possible effects of RAI with your doctor so that you know what to expect. On the first day of treatment, you might experience nausea and vomiting and occasionally pain and swelling can occur in the areas where the radioactive iodine typically collects, such as salivary glands. This can cause dry mouth and taste disturbance.
Large or cumulative doses of irradiation may mean you are unable to produce a child, especially in men, where decreased sperm counts and infertility have been reported for approximately two years. It is recommended that women avoid pregnancy for at least one year after radioiodine therapy and they should avoid breast-feeding. There is an increased risk of secondary cancers with the use of repetitive courses of radioactive iodine (see life-long follow-up).
Thyroid Stimulating Hormone (TSH) increase in preparation for ablation
For ablation to be successful, your thyroid gland cells need to be able to absorb lots of iodine. To make them as “iodine hungry” as possible, you may be asked to minimise iodine in your diet in the weeks before ablation. Importantly, your remaining thyroid and thyroid tumour cells can be stimulated to take up iodine with high levels of the so called thyroid stimulating hormone (TSH) in your body.
Your doctor will therefore want to raise TSH levels in your body by either giving you injections of bioengineered TSH (recombinant human TSH, rhTSH) or by temporarily stopping your thyroid hormone tablets. If you stop taking your thyroid hormone tablets, you will likely experience side effects due to low levels of thyroid hormone in your body – this is called hypothyroidism. 4 The most commonly reported side effects of rhTSH are nausea (12%) and headache (7%).
Thyroid hormone withdrawal
If you and your doctor decide to stop your thyroid hormone tablets in order to raise your TSH levels in your blood, this will happen two to six weeks before ablation (a minimum level of TSH is required for ablation to be successful).
During this time you are likely to feel listless and tired; you might suffer from bouts of fatigue, and may experience difficulty concentrating. Some patients also struggle with depression and memory. You may need to take time off work during this phase of your treatment.
Common side effects of hypothyroidism
Injections of rhTSH
This approach achieves a rapid short-term increase in levels of TSH and involves being given an intra-muscular injection on each of the two days before ablation while still taking your thyroid hormone tablets. This avoids the unpleasant effects of stopping your hormone tablets and may shorten the period between surgery and ablation by 10-14 days. The most commonly reported side effects of rhTSH are nausea (12%) and headache (7%).
Thanks to advanced treatment options the symptoms of hypothyroidism after thyroid surgery or during follow-up care are greatly reduced, and radioiodine treatment times can be shortened to a minimum; the first course of radioiodine therapy can be completed just 14 days after surgery.