What is Radioactive Iodine Total Body Scan? How Does It Show the Tumor Focus?

Theranostics is a recently developing field of the medicine. This approach takes body images using a tumor-specific agent to locate the tumor and its metastasis and their potential future locations and it also uses a specific agent with pre-determined therapeutic efficiency for the diseased tissue. This approach enables switching from traditional medicine to contemporary personalized medical procedures.

Administration of low-dose radioactive iodine (I-131 or I-123) to obtain images with high sensitivity and specificity of tumor tissues for diagnostic purposes combined with high-dose radioactive iodine (I-131) for specific and targeted treatment of these tumors is the oldest known example of theranostic practices in thyroid cancer.

Thyroid tissue has a unique ability to collect all iodine from the bloodstream and store it in the gland. Similar to iodine, radioactive iodine accumulates in the thyroid gland and it is stored in thyroid tissues. Differentiated thyroid cancers also have this characteristic that is less potent than that of healthy thyroid tissue.

Who is Eligible For Radioactive Iodine Total Body Scan?

Radioactive iodine total body scan is performed for patients with differentiated thyroid cancer upon request of the primary physician (who follows up the patient) for the following reasons:

  • Evaluating and assessing the uptake in the neck following thyroid surgery and before radioactive iodine treatment.
  • Imaging after treatment with radioactive iodine.
  • Monitoring of patients with moderate or high risk of recurrent thyroid cancer.

    Is Radioactive Iodine Total Body Scan Safe?

    Radioactive iodine total body scan is a safe imaging modality, which is performed by administering radioactive iodine isotopes at low diagnostic dosage before the treatment.

    Radioactive iodine total body scan is contraindicated to pregnant patients. For nursing mothers it might be necessary to stop breastfeeding.     

    Preparation before Radioactive Iodine Total Body Scan

    Our Nuclear Medicine Specialist will review your medical history regarding your thyroid gland, surgery/pathology reports, past imaging results and blood tests as well as doses administered in the course of past radioactive iodine treatments and s/he will also perform a physical examination and request certain blood tests, when necessary, before the radioactive iodine total body scan.

    Moreover, a beta-hCG test will be ordered for all women of child-bearing age.

    You will need special preparation before the treatment since thyroid hormones (LT4, LT3) and medicines and food which contain iodine affect the success of radioactive iodine total body scan.

    You will get information and guidance about this issue during the appointment. Your strict compliance with these suggestions is very important for successful imaging.

    Cessation of Thyroid Hormone Replacement

    If it is planned to stop thyroid hormone supplements before the radioactive iodine total body scan, our Nuclear Medicine Specialist will plan the necessary replacement cessation schedule.

    Administration of LT4 hormone supplements (i.e. Levotiron, Tefor, Euthrox, and Bitiron) should be stopped for at least 4 weeks and LT3 hormone supplements (i.e. Tiromel) should be stopped for at least 2 weeks.

    Use of Recombinant TSH (rhTSH)

    rhTSH (Thyrogen) is administered to hip muscle in 2 doses at 24-hour interval as an alternative to cessation of thyroid hormone replacement. Radioactive iodine is administered by mouth 24 hours after the last dose of rhTSH.

    Low-Iodine Diet

    Low iodine diet is an important component of preparation for the radioactive iodine total body scan and it is started 2 weeks in advance and maintained for 1 to 2 days after the treatment. This diet increases the success rate of radioactive iodine total body scan.

    Medicines Which Prevent Administration of Radioactive Iodine


    Recommended Duration of Cessation

    Thionamide medications (i.e. Propylthiouracil, methimazole, carbimazole)

    3 days

    Multivitamins that contain iodine

    7-10 days

    For natural/synthetic thyroid hormones, triiodothyronine (LT3 ,Tiromel)

    10-14 days

    For natural / synthetic thyroid hormones, thyroxin (LT4, Levotiron, Tefor, Euthrox, Bitiron)

    3-4 weeks

    Kelp, agar, carrageenan, Lugol solution

    2-3 weeks, depending on the iodine content

    Saturated solution of Potassium iodure

    2-3 weeks

    Topical iodine (i.e. surgical skin preparation)

    2-3 weeks

    Intravenous radiographic contrast agent, water-soluble

    6-8 weeks

    Intravenous radiographic contrast agent, fat-soluble

    1-6 months


    3-6 months or longer

    Hair dye (containing iodine)

    8 weeks

    Food Products Which Will Be Stopped For 2 Weeks Due To High Concentration of Iodine



    Iodized salt


    Dairy products

    Milk, yoghurt, cheese, ice cream

    Egg yolk

    Egg whites could be consumed.

    Sea foods

    Shellfishes and fishes, excluding tuna fish

    Turkey and liver


    Algae and algae products

    Carrageenan and alginate

    Milk chocolate


    Multivitamins that contain iodine


    Products which contain red food dye (E127, erythrocyte ) (etc. hair dye, fizzy drink)



    It could be consumed in small servings (1/4 of a plate) per meal.


    Allowed Foods

    Fresh fruit and vegetables

    Salt-free peanuts/hazelnuts and hazelnut/peanut butter

    Egg (white)

    Fresh meat

    Cereals/cereal products which do not contain iodine at high concentration (limited to 4 servings per day)

    Pasta, which do not contain iodine at high concentrations





    Black pepper

    Fresh or dried weeds and spices

    All vegetable oils [including soy oil]

    Soda (which do not contain Red dye (E127))

    Coke, Diet coke

    Coffee (Not instant)

    Tea (Not instant)


    Fruit juices

    How is Radioactive Iodine Total Body Scan Performed?

    Oral food and water intake should be stopped for 4-6 hours before radioactive iodine is administered and this restriction should be maintained for approximately 2 hours after the treatment. 

    Radioactive iodine (I-131 or I-123:185 Mbq (5 mCi)) is in liquid or capsule form; it is administered by mouth at outpatient settings in the Nuclear Medicine Clinic.  

    Images are obtained in the Nuclear Medicine Clinic 48 to 72 hours after administration of radioactive iodine.

    Patients with normal renal functions are recommended to drink 2.5-3 liters of liquid (except for milk) and void frequently for 3 days following the radioactive iodine treatment. Thus, radiation exposure for the urinary bladder and salivary glands can be minimized.

    Defecation at least once a day throughout the procedure is important for minimizing the radiation exposure for your bowels and to increase the quality of images. You may use mild laxatives in case of constipation.

    You should flush twice every time after you use the toilet for the first 3-5 days. It is necessary for our male patients to urinate while sitting on the toilet during this period. It is necessary for you to wash your hands carefully following each visit to the bathroom to eliminate radioactive contamination. It is necessary to take a shower daily and to wash towels, underwear and clothes separately for the first 3-5 days. It is necessary for you to wash your hands before meals, reading or holding something for the first 3 to 5 days. Prefer paper tissues instead of cloth and dispose the tissues by flushing them through the toilet rather than throwing it to a trash can during this period of time.

    It is necessary for our patients, who received I-131 radio-isotope, to comply with certain rules to protect their relatives from unnecessary radiation exposure. These restrictions, which are recommended by the Turkish Atomic Energy Authority (TAEK), are written below, although they depend on the dosage, but detailed explanations will be provided by our Nuclear Medicine Specialist.

    Please contact us for further details.