Tuesday, May 12, 2009

Radioactive Iodine in the Diagnostic Process: Understanding I-123 Scans

When my then 21 year old diabetic daughter (pictured here) was formally diagnosed with thyroid cancer after a radical thyroidectomy on March 31, 2008 I had no idea what that would mean for her and her dreams as a young woman already dealing with a chronic health condition. She went into surgery to have thyroid nodules removed that had grown over the course of 4 years (after a number of inconclusive fine needle biospies) making it difficult for her to swallow and breathe.

The recovery room nurse whom I had met a year earlier and had come to know well when my daughter's father was diagnosed with stage IV esophageal cancer called me in to my daughter's bedside and explained that the surgeon performed a "more extensive surgery" than originally planned because "the thyroid was obviously malignant". Soon the surgeon came in and explained that waiting for the pathology report would be a formality for clinical confirmation but that the oncology department would have an endocrine oncology specialist consult the "case" during the course of my daughter's hospital stay.

I had never, before that moment, heard of 'thyroid cancer' in someone so young but we had "experienced" her fathers stage IV esophageal cancer treatment the year before and, in 2006, provided in-home hospice care for my father (her grandfather) diagnosed with terminal cancer after surviving leiomyosarcoma in 1998. Questions flooded my mind at the speed of lighting as I cried quietly while the doctors voice faded away and I could hear him no more; Would she have chemotherapy ? or radiation ? How about her voice ? Would she be able to talk ? Could she swallow again or would she need a feeding tube for survival like her father after receiving treatment for esophageal cancer. How about wound care ? How long would it take for her to heal as a diabetic ?

A ferocious maternal instinct kicked in almost instantly and I set out to learn as much as I could as fast as I could to take control of the situation and save my daughter from all the patient care and advocacy mistakes I made years earlier as my father's primary caregiver and healthcare proxy. Here I will share a summary review of what I learned about radioactive iodine uses for diagnostic testing of thyroid diseases (I-123) and the treatment of thyroid cancer (I-131).

Let's begin with I-123 in the diagnostic process also known as thyroid scan or radioactive iodine uptake test (RAIU)


Iodine is essential for proper function of the thyroid gland, which uses it to make the thyroid hormones our body relies on for proper metabolic function and other systematic biological functions such as heart rate, body temperature, calcium absorption, the reproductive system and more. The thyroid is equipped with an active system or "pump" for moving iodine into it's cells. Thyroid cancer cells usually take up iodine also, "although they do not this as well as normal thyroid cells".The ability of thyroid cells to take up iodine has been used by medical professionals to treat various thyroid diseases for decades.


A radioactive isotope is a substance that gives off radiation. Iodine can be made into two radioactive isotopes for medical uses: I-123 and I-131. These isotopes can be given by mouth to patients with suspected thyroid conditions. RAI is then concentrated inside the thyroid cells exactly like iodine and can be used to diagnose or treat thyroid problems. The radiation that RAI gives off can either be harmless to the thyroid cells (I-123) or the radiation my destroy the thyroid cells (I-131). RAI that is not concentrated in the thyroid gland is eliminated from the body through sweat and urine. RAI is safe to use in individuals who have had an allergic reaction to seafood or X-Ray contrast agents, since the allergic reaction is to the compound continaing iodine, not the iodine itself.


I-123 is the isotope used to take the pictures of the thyroid gland during a Thyroid Scan. A very small "tracer" dose of I-123 is given to the patient, who then returns 3-8 hours later so "pictures" of the thyroid gland can be taken using a "camera" that picks up the radiation emitted by the RAI. The "camera" is part of a machine that looks similar to an X-Ray or CAT Scan machine. In addition to getting the scan or picture, the amount of radiation being given off can also be counted to determine how "active" the thyroid gland is also know as a Radioactive Iodine Uptake (RAIU). Since the radiation emitted by I-123 is harmless, no special precautions are necessary after a thyroid scan or RAIU. The total radiation iodine dose that you receive during a thyroid scan is less than you would get if you had a routine chest x-ray. There are usually no side effects to I-123.


About The Author: Wilma Ariza is the Founder of Stevie JoEllie's Cancer Care Fund a thyroid cancer awareness, access to care and free supportive services for thyroid cancer patients and survivors nonprofit. 

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