|Fig. 1: Example of thyroid cancer in which RAI may be used as treatment. (Source: Wikimedia Commons)|
Radiation is both a risk-factor for thyroid cancer and, as a contrast, also instrumental in its treatment. As other cancer types have declined, thyroid cancer is unpredictably climbing and can metastasize to other cells. (see Fig. 1.) As a result, it is becoming increasingly essential to both understand this cancer's causes as well as its therapies and cures. Scientists now believe that genetics plays a role in the occurrence of thyroid cancer and are determined to research the connection as this type of cancer rises in contrast to other cancers. Yet, while the occurrences rise, early detection and treatment has allowed the death rate to remain fairly low.  The escalation of thyroid cancer is causing significant attention and rising funding for research of successful treatment.
Optional treatments include surgery, thyroid hormone therapy, external beam radiation therapy, chemotherapy, and targeted therapy. Radioactive Iodine Therapy (RAI), has proven to be a successful therapy in fighting this rising type of cancer, mostly as a follow up to initial thyroid surgery. 
Radioactive Iodine Therapy occurs internally by ingesting a radioactive form of iodine called Iodine 131 (I-131). The bloodstream picks up this iodine and circulates it throughout the body. The radioactive iodine is principally absorbed by the cells in the thyroid and no other cells are generally exposed to radiation. Both healthy and cancerous thyroid cells take up the radioactive iodine and are demolished or damaged. Cancerous cells of the thyroid, however, are not as receptive to the radioactive iodine as much as healthy thyroid cells.  In low number of cases, a person's thyroid may be very resistant to absorbing iodine at all and this therapy may not be as effective. An extreme case of thyroid cancer may result in obvious and distorted neck enlargement due to swelling, sick thyroid cells as shown in Fig. 2.
|Fig. 2: Extreme case of thyroid cancer. (Source: Wikimedia Commons)|
To encourage the thyroid cells that are unhealthy with cancer to absorb this iodine, there are two common strategies utilized, one of which is to increase the levels of thyroid stimulating hormone (TSH). Increasing the levels of TSH stimulates the sick thyroid cancer cells to more actively absorb iodine than is normal. Stopping hormone replacement therapy or by using synthetic human recombinant TSH, initiates higher levels of TSH through the pituitary gland. In this way, the cancerous cells more willingly absorb the radioactive iodine and are destroyed.  The second strategy to encourage thyroid cells to absorb the iodine is to reduce iodine levels in the body with a low-iodine diet which is also effective. Eventually all the thyroid cells, including the cancerous sick cells, will more actively absorb the radioactive iodine.
After the body has prepared to absorb more radioactive iodine, an initial check of administering iodine will enable the doctor to know how much of the thyroid cells still remain by measuring the amount of iodine absorbed in the neck area. It is also helpful to receive a small amount of radioactive iodine to determine how much thyroid tissue is left in the neck and even outside the thyroid.  At this point, it will be determined how much radioactive should be administered to destroy all thyroid material left, and also any other cancer cells that may have developed around that area. This process can occur up to three times until the cancerous thyroid cells are obliterated.
Preventative measures must be taken after treatment to avoid others being exposed to radiation. These should include sleeping alone and avoiding contact for up to a week after treatment. The patient should stay at least six feet away from anyone for at least three days. Avoiding all sharing of items and eating utensils should occur along with daily showers and multiple hand washing by the patient. A treated patient's sweat and urine will be radioactive after therapy for up to a week and flooding the body with water will stimulate the body to eliminate the radioactive iodine through urine.  Women are warned not to become pregnant within six months after therapy nor breastfeed.  Furthermore, women cannot be pregnant during treatment and the chances of becoming pregnant may be decreased. 
Preventative measures must be taken after treatment to avoid others being exposed to radiation. These should include sleeping alone and avoiding contact for up to a week or two after treatment.  The patient should stay at least six feet away from anyone for at least three days. Avoiding all sharing of items and eating utensils should occur along with daily showers and multiple hand washing by the patient. A treated patient's sweat and urine will be radioactive after therapy for up to a week and flooding the body with water will stimulate the body to eliminate the radioactive iodine through urine.  Women are warned not to become pregnant within six months after therapy nor breastfeed.  Furthermore, women cannot be pregnant during treatment and the chances of becoming pregnant may be decreased. 
Side effects or RAI treatment may include salivary gland inflammation, dry mouth, general swelling and inflammation of the mouth as well as taste and smell having short term issues. Swelling and neck pain are uncommon but can occur and in contrast, nausea is often reported.  All resulting symptoms may be treated to reduce their effect. However, other long-term effects may be more worrisome.
RAI Therapy has both adverse effects and many possible long-term effects.  Long-term outcomes of RAI therapy include temporary reduction in testosterone in men and stopping of periods or a heavier period in women. General tiredness can be a plaguing outcome while dry or watery eyes may result due to eye glands being impacted. Lung problems may occur and will need to be monitored and bone marrow behavior may be interrupted as well.  Of greater concern is that children or young adults may have higher occurrences of a second primary malignancy. So far, only case studies have documented the risk to children and young adults, but there is a significant higher risk to develop a secondary primary cancer that is directly due to the treatment of the radioactive iodine. Secondary tumors are a general risk overall while research has shown the leukemia form of cancer is also a risk. 
Radioactive Iodine Therapy is generally accepted as a follow up to thyroid surgery to kill remaining thyroid cells which may be cancerous. However, this therapy remains controversial when applied to less advanced thyroid cancer and cancer in young children and adults because of the long-term effects which include an unexpected higher risk of secondary cancer.  When smaller tumors, though, have troublesome characteristics such as aggression, blood vessel invasion or multiple locations, RAI may be recommended despite long-term risks.  There even exists cost-cutting pressures at hospitals as well as concerns that doctors and patients do not have the correct scientific results to make the decision for this therapy. [1,2] In fact, it appears that decisions to use this therapy may even rest on the patient or doctor preferences rather than scientific studies.  In a sense, there is an over- diagnosis of insignificant cancer that should be treated with alternative safer therapies making RAI unnecessary and causing further future risk. 
Currently, RAI is considered a good therapy for higher stage levels of thyroid cancer and less for lower stage levels, or newer, less invasive thyroid cancer. Alternative therapies effectively fight the newer, less invasive thyroid cancer in early stages, do less long-term risk, and cut costs that have proven unnecessary for this expensive therapy.
© Kyle Gilbert. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 M. Crane, "New Cases of Thyroid Cancers Up," The Columbus Dispatch, 12 Jan 14.
 M. R Haymart et al., "Use of Radioactive Iodine for Thyroid Cancer," J. Amer. Med. Assoc. 306, 721 (2011).
 S. Sternberg and A. DeBarros, "It Kills Thyroid Cancer, But Is Radiation Safe?," USA Today, 28 May 08.
 F. Pacini et al., "Radioactive Iodine-Refractory Differentiated Thyroid Cancer: Unmet Needs and Future Directions," Expert Rev. Endocrinol. Metab. 7, 541 (2008).
 M. Luster et al., "Guidelines for Radioiodine Therapy of Differentiated Thyroid Cancer," Eur. J. Nucl. Med. Mol. Imaging 35, 1941 (2008).
 J. Goodwin, "Some Thyroid Cancer Patients May Get Radioactive Iodine Unnecessarily," U.S. News, 16 Aug 11.