How To Prepare For The Test
Follow instructions about not eating before the test. You may be told not to eat after midnight the night before your test.
Your health care provider will tell you if you need to stop taking medicines before the test that may affect your test results. DO NOT stop taking any medicine without first talking to your provider.
Tell your provider if you have:
- Had recent CT scans using intravenous or oral iodine-based contrast
- Too little or too much iodine in your diet
What Is A Radioactive Iodine Uptake Test
The radioactive iodine uptake test involves using a small amount of radioactive iodine and a gamma camera to detect cancer cells in the thyroid gland.
For the procedure, the patient swallows a capsule of I-123, which is absorbed by the thyroid gland. Using a gamma camera, the front of the patients neck is imaged several hours later to determine where and how the radioactive iodine has accumulated. Thyroid cancer cells absorb more iodine than surrounding tissue.
To detect thyroid cells located elsewhere in the body, the gamma camera will scan the entire body .
Radioiodine scans are also used in the care and management of patients with differentiated thyroid cancer, which includes papillary, follicular and Hurthle cell thyroid cancers.
Radioactive Iodine Therapy For Thyroid Cancer
Your thyroid gland absorbs nearly all of the iodine in your body. Because of this, radioactive iodine can be used to treat thyroid cancer. The RAI collects mainly in thyroid cells, where the radiation can destroy the thyroid gland and any other thyroid cells that take up iodine, with little effect on the rest of your body. The radiation dose used here is much stronger than the one used in radioiodine scans, which are described in Tests for Thyroid Cancer.
This treatment can be used to ablate any thyroid tissue not removed by surgery or to treat some types of thyroid cancer that have spread to lymph nodes and other parts of the body.
Radioactive iodine therapy helps people live longer if they have papillary or follicular thyroid cancer that has spread to the neck or other body parts, and it is now standard practice in such cases. But the benefits of RAI therapy are less clear for people with small cancers of the thyroid gland that do not seem to have spread, which can often be removed completely with surgery. Discuss your risks and benefits of RAI therapy with your doctor. Radioactive iodine therapy cannot be used to treat anaplastic and medullary thyroid carcinomas because these types of cancer do not take up iodine.
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Preparing For Rai Therapy
For RAI therapy to be most effective, you must have a high level of thyroid-stimulating hormone in the blood. This hormone is what makes thyroid tissue take up radioactive iodine. If your thyroid has been removed, there are a couple of ways to raise TSH levels before being treated with RAI:
- One way is to stop taking thyroid hormone pills for several weeks. This causes very low thyroid hormone levels , which makes the pituitary gland to release more TSH. This intentional hypothyroidism is temporary, but it often causes symptoms like tiredness, depression, weight gain, constipation, muscle aches, and reduced concentration.
- Another way is to get an injection of thyrotropin , which can make withholding thyroid hormone for a long period of time unnecessary. This drug is given daily for 2 days, followed by RAI on the 3rd day.
Most doctors also recommend that you follow a low iodine diet for 1 or 2 weeks before treatment. This means avoiding foods that contain iodized salt and red dye #3, as well as dairy products, eggs, seafood, and soy.
How Is The Procedure Performed
Doctors perform nuclear medicine exams on outpatients and hospitalized patients.
Thyroid Scan
You will lie on an exam table. If necessary, a nurse or technologist will insert an intravenous catheter into a vein in your hand or arm.
For most exams, you will receive an injection of the radiotracer. Or, you may swallow it or inhale it as a gas.
When radiotracer is taken by mouth, in either liquid or capsule form, it is typically swallowed up to 24 hours before the scan. The radiotracer given by intravenous injection is usually given up to 30 minutes prior to the test.
When it is time for the imaging to begin, you will lie down on a moveable examination table with your head tipped backward and neck extended. The gamma camera will then take a series of images, capturing images of the thyroid gland from three different angles. You will need to remain still for brief periods of time while the camera is taking pictures.
After the exam, you may need to wait until the technologist determines if more images are needed. Sometimes, the technologist takes more images to clarify or better visualize certain areas or structures. The need for more images does not necessarily mean there was a problem with the exam or that something is abnormal. It should not cause you concern.
If you have an intravenous line for the procedure, your technologist will usually remove it. The technologist will leave it in place if you are to have another procedure that same day that requires an IV line.
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What Is The Prognosis Of Thyroid Cancer
Overall, your prognosis with differentiated thyroid cancer is excellent, especially if you are younger than 55 years of age and have a small cancer. If your papillary thyroid cancer has not spread beyond the thyroid gland, patients like you rarely if ever die from thyroid cancer. If you are older than 55 years of age, or have a larger or more aggressive tumor, your prognosis remains very good, but the risk of cancer recurrence is higher. The prognosis may not be quite as good if your cancer is more advanced and cannot be completely removed with surgery or destroyed with radioactive iodine treatment. Nonetheless, even if this is your situation, you will likely be able to live a long time and feel well, despite the fact that you are living with cancer. It is important to talk to your doctor about your individual profile of cancer and expected prognosis. It will be necessary to have lifelong monitoring, even after successful treatment.
Plan For Transportation After Treatment
Radioactive iodine gives off radiation. This means that after your treatment, you wont be able to go home using public transportation such as buses, the subway, trains, or a plane. You can drive yourself home, have someone pick you up and take you home, or take a taxi or private car home. See our Resources section for information about car services.
Make a plan for getting home before you come for your treatment.
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How Does Radioactive Iodine Treat Thyroid Cancer
The most common types of thyroid cancer can usually be treated with large doses of radioactive iodine. The therapy is usually given after removal of the thyroid gland to destroy any remaining thyroid tissue.
A tracer dose of radioactive iodine can also be used to track remaining thyroid tissue and/or cancer that could have spread to other parts of the body. These tests show if iodine concentrates in areas that contain thyroid cancer, and whether large amounts of RAI are needed to destroy the tumor implants.
What Abnormal Results Mean
Higher-than-normal uptake may be due to an overactive thyroid gland. The most common cause is Graves disease.
Other conditions can cause some areas of higher-than-normal uptake in the thyroid gland. These include:
- An enlarged thyroid gland that contains nodules producing too much thyroid hormone
- A single thyroid nodule that is producing too much thyroid hormone
These conditions often result in normal uptake, but the uptake is concentrated into a few areas while the rest of the thyroid gland does not take up any iodine . This can only be determined if the scan is done along with the uptake test.
Lower-than-normal uptake may be due to:
- Factitious hyperthyroidism
- Iodine overload
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Follicular Thyroid Cancer Treatment With Rai : How And How Much Treatment
Follicular thyroid cancer guidelines for post operative treatment with radioactive iodine were last updated in the American Thyroid Association 2015 edition. Some endocrinologists and nuclear medicine specialists order a preliminary nuclear study called a thyroid cancer uptake study. After your doctor has prepared your body for RAI by either stopping your use of thyroid hormone pills or giving injections of recombinant TSH , they may choose to give you a small dose of RAI and perform a special nuclear scan called a Thyroid Cancer Uptake Study. This is a very low quantity of radioactive iodine and may be I131 or I123. In most cases, it is done the day before the higher dose RAI treatment.
There are several potential benefits in obtaining a Thyroid Cancer Uptake Study:
- 1)The follicular thyroid cancer’s ability to produce the blood marker thyroglobulin is determined while the patient is in a hypothyroid state . This is called a stimulated thyroglobulin level. This gives the thyroid cancer team a good “feel” for whether you any disease whatsoever and the likelihood for cure. 2)Where the follicular thyroid cancer exists in the body and how much of the swallowed dose or radioactive iodine is taken up by the cancer is able to be determined by the nuclear scan. 3)The thyroid cancer uptake study can be utilized to determine the optimal dose of the radioactive iodine treatment the following day.
Some argue against obtaining Thyroid Cancer Uptake Studies because:
What Else Should I Know About A Nuclear Scan
- The radiation exposure from a nuclear scan comes from the radionuclides used the scanner itself does not put out radiation. The radioactive material in your body will naturally decay and lose its radioactivity over time. It may also leave your body through your urine or stool within a few hours or a few days. Talk to your health care team about whether you need to take precautions about having sex, or being close to children or pregnant women after these tests.
- You will be asked to drink a lot of water to flush out the radioactive material.
- To reduce the risk of being exposed to radioactive material in your urine after a scan, you should put the lid down and flush the toilet right after you use it.
- Nuclear scans are rarely recommended for pregnant women, so let your doctor know if you are or might be pregnant.
- If you are breastfeeding, be sure to tell the doctor ahead of time. You may need to pump breast milk and discard it until the radionuclide is gone from your system.
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Radiation Therapy And Radiation Exposure
People who undergo radiation therapy in infancy or childhood for conditions such as an enlarged thymus, tonsils, or adenoids may develop thyroid cancer. According to experts, cancer can develop as early as 5 years after radiation therapy or 20 or more years later.
Exposure to radiation from nuclear fallout is also associated with a high risk of thyroid cancer, especially in children.
What Is A Thyroid Scan
Definition:A thyroid scan is a nuclear medicine examination that uses the emissions of gamma rays from radioactive iodine to help determine whether a patient has thyroid problems, including hyperthyroidism, cancer, or other growths.
Alternative Names: Scan – thyroid Radioactive iodine screening test – thyroid RAUI Nuclear scan – thyroid
How the test is performed:You will be given a pill that contains radioactive iodine, and then you will wait as the iodine collects in the thyroid. The first scan is usually 4 – 6 hours after the iodine has been ingested, and another scan may be taken 24-hours later. Additional or substitute imaging may be performed using a compound containing technetium.
After the radioiactive iodine has been absorbed by the thyroid, you will lie on your back on a movable table with your neck and chest positioned under the scanner. The scanner detects the location and intensity of the gamma rays emitted. During this part of the procedure, you must lie still to let the scanner get a clear image.
Next, the information is sent to a computer that displays images of the thyroid and any possible nodules that have absorbed the iodine.
How the test will feel:Some patients find remaining still during the test uncomfortable.
Why the test is performed:When thyroid cancer or nodules are suspected.
Normal Values:The thyroid appears the correct size, shape, and in the proper location. It appears a uniform gray on the computer.
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How Should I Prepare
You may wear a gown during the exam or be allowed to wear your own clothing.
Women should always tell their doctor and technologist if they are pregnant or breastfeeding. See the Safety in X-ray, Interventional Radiology and Nuclear Medicine Procedures page for more information about pregnancy and breastfeeding related to nuclear medicine imaging.
Tell the doctor and your exam technologist about any medications you are taking, including vitamins and herbal supplements. List any allergies, recent illnesses, and other medical conditions.
You should tell your physician if you:
- have had any tests, such as an x-ray or CT scan, surgeries or treatments using iodinated contrast material within the last two months.
- are taking medications or ingesting other substances that contain iodine, including kelp, seaweed, cough syrups, multivitamins or heart medications.
- have any allergies to iodine, medications and anesthetics.
- are breastfeeding.
In the days prior to your examination, blood tests may be performed to measure the level of thyroid hormones in your blood. You may be told not to eat for several hours before your exam because eating can affect the accuracy of the uptake measurement.
Leave jewelry and accessories at home or remove them prior to the exam. These objects may interfere with the procedure.
Your doctor will tell you how to prepare for your specific exam.
Medical History And Physical Exam
If you have any signs or symptoms that suggest you might have thyroid cancer, your health care professional will want to know your complete medical history. You will be asked questions about your possible risk factors, symptoms, and any other health problems or concerns. If someone in your family has had thyroid cancer or tumors called pheochromocytomas, it is important to tell your doctor, as you might be at high risk for this disease.
Your doctor will examine you to get more information about possible signs of thyroid cancer and other health problems. During the exam, the doctor will pay special attention to the size and firmness of your thyroid and any enlarged lymph nodes in your neck.
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Magnetic Resonance Imaging Scan
MRI scans use magnets instead of radiation to create detailed cross-sectional images of your body. MRI can be used to look for cancer in the thyroid, or cancer that has spread to nearby or distant parts of the body. But ultrasound is usually the first choice for looking at the thyroid. MRI can provide very detailed images of soft tissues such as the thyroid gland. MRI scans are also very helpful in looking at the brain and spinal cord.
What Is Radioactive Iodine Therapy
Radioactive iodine can be used for the treatment of overactive thyroid and certain types of thyroid cancer. The term radioactive may sound frightening, but it is a safe, generally well-tolerated, and reliable treatment that targets thyroid cells so there is little exposure to the rest of your bodys cells.
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How Does The Procedure Work
Ordinary x-ray exams pass x-rays through the body to create an image. Nuclear medicine uses radioactive materials called radiopharmaceuticals or radiotracers. Your doctor typically injects this material into your bloodstream. Or you may swallow it or inhale it as a gas. The material accumulates in the area under examination, where it gives off gamma rays. Special cameras detect this energy and, with the help of a computer, create pictures that detail how your organs and tissues look and function.
What Causes Thyroid Cancer
Thyroid cancer is more common in people who have a history of exposure to high doses of radiation, have a family history of thyroid cancer, and are older than 40 years of age. However, for most people, we dont know why thyroid cancer develops.
High dose radiation exposure, especially during childhood, increases the risk of developing thyroid cancer. Radiation therapy used to treat cancers such as Hodgkins disease or breast cancer has been associated with an increased risk for developing thyroid cancer if the treatment included exposure to the head, neck or chest. Routine X-ray exposure such as dental X-rays, chest X-rays and mammograms are not associated with a high risk of thyroid cancer. As always, you should minimize radiation exposure by only having tests which are medically necessary.
Exposure to radioactivity released during nuclear disasters has also been associated with an increased risk of developing thyroid cancer, particularly in exposed children, and thyroid cancers can be seen in exposed individuals as many as 40 years after exposure.
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What Are The Limitations Of The Thyroid Scan And Uptake
The thyroid scan and thyroid uptake are not performed on patients who are pregnant because of the risk of exposing the fetus to radiation. These tests are also not recommended for breastfeeding women.
Nuclear medicine procedures can be time consuming. It can take several hours to days for the radiotracer to accumulate in the area of interest. Plus, imaging may take up to several hours to perform. In some cases, newer equipment can substantially shorten the procedure time.
The image resolution of nuclear medicine images may not be as high as that of CT or MRI. However, nuclear medicine scans are more sensitive for a variety of indications. The functional information they yield is often unobtainable using other imaging techniques.