Radioiodine therapy for thyroid cancer (General Information)

Radioiodine Therapy For Thyroid Cancer (General Information)

Thyroid cells have the capacity to take up iodine and iodine is essential for the growth and function of thyroid cells. This principle is utilized in radioiodine treatment of thyroid cancers after initial surgery. Radioactive iodine (called I¹³¹) can seek out and destroy any remaining thyroid cells (including normal and cancer cells) that may be invisible at the time of surgery and are inadvertently left behind.  I¹³¹ therapy is associated with reduced risk of recurrent thyroid cancer. Typically I¹³¹ therapy is followed by a whole body scan in 5-7 days. After the scan, patient starts taking Synthroid^® (levothyroxine). Patient should be on a low iodine diet for ~14 days before the I¹³¹ therapy. Iodine is found in variable amounts in all food and beverages. The highest sources (and therefore those to be avoided during this 14-day period) are iodized salt, grains, cereals, some breads, fish from the sea, shellfish, beef, processed meats, milk and milk products. You can find useful details on www.thyca.org and www.thyroid.org. This diet is generally continued until the whole body scan is completed (7 days after the I¹³¹ is given). After I¹³¹ you should observe appropriate precautions to avoid radiation exposure to others. 

For successful I¹³¹ therapy, blood level of a hormone called TSH should be high & the patient should have very low circulating level of natural iodine.  

There are two ways of raising blood TSH level.  

1. By stopping thyroid tablets. Typically, a short-acting thyroid “pill” called Cytomel^® (T₃) is given after thyroid surgery for 4 weeks and then stopped for ~10-14 days (to prepare for I¹³¹ therapy). Patients may develop swelling, fatigue, aches during these 14 days.  I¹³¹ is given after TSH is confirmed to be high.  

2. By Thyrogen^® method. Thyrogen is synthetic human TSH and is administered as 2 injections which raise TSH without the need to stop thyroid tablet. I¹³¹ is then given 24 hours later. A blood test (tumor marker called TG-thyroglobulin) is taken 48 hrs after that and “scan” is done 5-7 days later. In this method, patient can start Synthroid immediately after surgery and does not have to tolerate the symptoms of hypothyroidism.   

I¹³¹ therapy is generally considered safe and very effective. There is a small risk of temporary or permanent damage to salivary glands.  A decrease in white blood cells is sometimes seen. Occasional patients may have nausea or neck discomfort. There is an extremely small increase in risk of secondary malignancies (leukemia etc) in some cases (usually dose dependent).  Women should avoid pregnancy or breast feeding for at least 6-12 months after I¹³¹ therapy. 

For more information: 

www.thyroid.org 

www.mythyroid.com/radioactiveiodinecancer.html 

www.thyrca.org 

www.thyrogen.com 

¤ Timeline for I¹³¹ Therapy(Thyrogen Method) 

Start low iodine diet     Start 10 days before the Thyrogen Injection 

Thyrogen injection #1 (Dr. Haque’s office) ______________Mon 

Thyrogen injection #2 (Dr. Haque’s office) ______________ Tue 

I¹³¹ radioactive pill (Nuclear Medicine Dept. Hospital) ______________ Wed 

Blood Test (Thyroglobulin level) (Laboratory) ______________ Fri 

I¹³¹ radioactive SCAN (Nuclear Medicine Dept. Hospital) _____________ Tue/Wed 

Resume normal diet _After Scan____  

¤ Timeline for I¹³¹ Therapy (Thyroid Withdrawl Method) 

Start low iodine diet _____________ 

Stop Cytomel ______________Wed 

Blood Test (TSH) ______________ Mon 

Office visit ______________ Tue 

I¹³¹ radioactive pill (Nuclear Medicine Dept. Hospital) ______________ Wed 

Blood Test (Thyroglobulin level) ______________ Fri 

I¹³¹ radioactive SCAN (Nuclear Medicine Dept. Hospital) _____________ Tue/Wed 

Start Synthroid and resume normal diet _After Scan____  

Blood tests are then done in 2 to 3 months to determine if you are on the right dose of    Synthroid.