Preparing for a 131 Iodine Whole Body Scan after Thyroidectomy for Cancer Thyroid

131 Iodine Whole body scan of a 28 year Female patient with papillary carcinoma of the thyroid gland after near total thyroidectomy. The faint blue - black color seen in the neck region signifies functioning residual thyroid tissue. The patient had a thyroglobulin value of 26 ng/ml and the patients TSH was 92uIU/ml

The 131 iodine whole body scan is usually performed after good preparation by administering a 2-3mCi of 131 iodine whole body capsule and the scan is acquired at 48 - 72 hours post administration. What you see above is the image of such a scan.  

What should be the preparation of such a patient be?

When a whole body iodine scintigraphy or scan is done for a patient after thyroidectomy (removal of the thyroid gland surgically) for thyroid cancer, it should be delayed for about 4 weeks from the time of surgery to allow endogenously secreted thyroid hormones to be metabolized and give time for the TSH (Thyroid Stimulating Hormone) secreted by the pituitary gland to rise to near 100 uIU/ml levels. 

• The patient should not have been administered with iodine contrast for a CT contrast study prior to surgery, which is currently never used and is only employed when the primary presentation is with some systemic condition other than thyroid swelling or nodule. If used the patient should wait about 3 months before the 131 iodine whole body scan to be done. 
• The other precaution is for the treating surgeon not to start the patient on Thyroid Hormone Supplements (Eltroxin or Thyronorm) immediately after surgery and to refer such patients to a nuclear medicine department for 131 iodine scan appointments preferably in the second week of surgery with the - discharge summary, thyroid biopsy slide & block, and the histopathology report. If a patient was started on thyroid medications then the patient has to stop these medication for about 4 weeks before the scan to allow - TSH hormone to rise to near 100 values. 
• After an appointment is given for an iodine 131 Whole body scan the patient is advised as follows as part of the preparation for the scan.

1. A low iodine containing diet is recommended for 2 weeks prior to the scan and continued until the therapy is over - if the therapy date is further from the date of the scan. Ideally a therapy to be scheduled on the same day as the scan is taken is ideal in reducing the post therapy stunning if any. This is generally seen in >5 mci doses of 131 Iodine being used for whole body scans, currently a standard dose of today's practice is to use is a 2-3mCi dose for a whole body iodine scan which negates this possibility. The best ablative results are obtained when the patient is ablated within 3 months post surgery. 
2. The patient should avoid Iodized salt and sea salt during this period as in [preparation for scan and therapy. this is to prevent the non radioactive iodine from blocking the 131 radioactive iodine from visualizing residual thyroid tissue or metastasis in the whole body scan. 
3. Numerous milk and dietary products are fortified with iodine and the patient should avoid any sort of fortified food - to be safer it is best to avoid these as part of preparation. 
4. Patients may also avoid Eggs, Seafood, Kelp, Breads with iodated dough conditioners, red food dyes, and restaurant foods since the content of iodine in these foods are also difficult to quantify and may vary in huge quantities.
5. The aim of this preparation is to successfully reduce urinary iodine to 50ug/day. A normal iodine excretion in urine would be 100 ug/day anything below 75ug/day would be considered as iodine deficiency. This means the patients iodine pool is depleted and when 131 iodine is administered to the patient it will or most likely pick up all the residual functioning thyroid tissue in the body. 
6. Normal faint uptakes of iodine are seen in the slavery glands, oral or nasal mucosa, stomach, colon urinary bladder. The liver 5-10 days after the administration of  radioactive iodine shows uptake and this is because the radioactive hormones produces are metabolized in the liver. 

• Dr Ajith Joy K, Consultant Nuclear Medicine Physician.