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HomeExclusiveWhich Radioisotope Is Used For Diagnosing Thyroid Disorders

Which Radioisotope Is Used For Diagnosing Thyroid Disorders

Nuclear Medicine: Radioisotopes For Diagnosis And Treatment

The risks of radioactive iodine treatment in thyroid cancer

One major use of radioisotopes is in nuclear medicine. Of the 30 million people who are hospitalized each year in the United States, 1/3 are treated with nuclear medicine. More than 10 million nuclear-medicine procedures are performed on patients and more than 100 million nuclear-medicine tests are performed each year in the United States alone. A comparable number of such procedures are performed in the rest of the world.

There are nearly one hundred radioisotopes whose beta and/or gamma radiation is used in diagnosis, therapy, or investigations in nuclear medicine. The most used radioisotopes were discovered before World War II using the early cyclotrons of Ernest Lawrence, with the initial applications to medicine being developed by his brother John Lawrence. Some of the most well known radioisotopes, discovered by Glenn Seaborg and his coworkers, are 131I , 60Co ,99mTc , and 137Cs . By 1970, 90 percent of the 8 million administrations per year of radioisotopes in the United States utilized either 131I, 60Co, or 99mTc. Today, 99mTc, with a half-life of 6 hours, is the workhorse of nuclear medicine. It accounts for more than 10 million diagnostic procedures a year in the United States. It is used for brain, bone, liver, spleen, kidney, lung and thyroid imaging as well as for blood-flow studies.

Fig. 13-3. a) PET scan image of the human brain. b) MRI image of the human brain.

Ionizing Radiation And Radiobiology

Nuclear medicine is the medical speciality that uses non-encapsulated sources of artificial ionizing radiation with diagnostic-therapeutic use and research. In these cases, the patient is the source of radiation. For these reasons, there is a risk of external radiation to health personnel, patients relatives and the general public. In addition, special attention is paid to the possibility of contamination because these tracers are excreted physiologically by tear secretions, saliva, sweat, urine, feces, genital fluids or breastfeeding.

Radiobiology studies the effects of ionizing radiation on cells. These effects are diverse and are classified into three large groups:

According to the time of appearance: early or late effects.

  • Depending on its action on cells: direct effects on DNA or indirect effects .

  • From a point of view of dose dependence: deterministic effects and stochastic effects .

  • Viii Closing Remarks Remaining Questions And Directions For Future Research

    Despite the accumulated knowledge during nearly 70 yr of study within the field of 131I therapy, our evidence base is hampered by most studies being inadequately designed and underpowered. Thus, to some surprise, high-level solid evidence is lacking for many aspects of this treatment. It is therefore difficult to provide well-founded recommendations. Evidently, the outcome from 131I therapy of hyperthyroid diseases is potentially confounded by a range of variables, such as age, goiter size, applied radioactive dose, severity and type of disease, as well as pre- and post-radioiodine use of ATD. Although most of the individual randomized trials did not find these drugs to be radioprotective, a reduction of the cure rate by the use of ATD in conjunction with 131I therapy is supported by a meta-analysis. Whether ATD have inherent radioprotective properties awaits additional well-powered and well-designed clinical trials and the utility of novel in vitro models. ATD also affect other factors such as serum TSH and the thyroid RAIU, and these may confound the influence of ATD on the cure rate after 131I therapy. Finally, the temporal relation between the treatment with ATD and the 131I administration needs to be taken into consideration and studied further.

    We are confident that the answers to these and many more questions will not await another 70 yr of study.

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    Recovery From A Thyroid Scan

    After your thyroid scan, you must contact your physician for instructions on how to resume taking your thyroid medication.

    The radioactive iodine in your body is passed when you urinate. You may be advised to drink extra fluids and empty your bladder often to flush out the radionuclide. You may need to be careful to protect others from potential exposure to the material. To do this, your doctor may advise you to flush twice after using the toilet for up to 48 hours after the test.

    You can typically resume your normal diet and activities immediately after any thyroid scan.

    What Are The Side Effects Of Radioactive Iodine


    Permanent hypothyroidism is an expected side effect of RAI treatment for hyperthyroidism. Fortunately, hypothyroidism is much easier to treat than hyperthyroidism using hormone replacement therapy. This is a lifelong treatment that is safe, reliable and inexpensive.

    Temporary side effects of RAI may include:

    • Neck tenderness and swelling.
    • Excessive tearing from the eyes.

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    Does Rai For Thyroid Imaging Provide The Best Results

    I-123 is the usual isotope used to take pictures and determine the activity of the intact thyroid gland , since it is harmless to thyroid cells. No special radiation precautions are necessary after a thyroid scan or RAIU using I-123. I-131 can also be used to take pictures of the thyroid gland, although it is rarely used due to the harmful effects it has on thyroid cells.

    Risks And Side Effects

    Your body will give off radiation for some time after you get RAI therapy. Depending on the dose of radioiodine used and where you are being treated, you might need to be in the hospital for a few days after treatment, staying in a special isolation room to prevent others from being exposed to radiation. Some people may not need to be hospitalized. Once you are allowed to go home after treatment, you will be given instructions on how to protect others from radiation exposure and how long you need to take these precautions. These instructions may vary slightly by treatment center. Be sure you understand the instructions before you leave the hospital.

    Short-term side effects of RAI treatment may include:

    Chewing gum or sucking on hard candy may help with salivary gland problems.

    Radioiodine treatment also reduces tear formation in some people, leading to dry eyes. If you wear contact lenses, ask your doctor how long you should keep them out.

    Men who receive large total doses of radiation because of many treatments with RAI may have lower sperm counts or, rarely, become infertile. Radioactive iodine may also affect a womans ovaries, and some women may have irregular periods for up to a year after treatment. Many doctors recommend that women avoid becoming pregnant for 6 months to a year after treatment. No ill effects have been noted in the children born to parents who received radioactive iodine in the past.

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    Iv Effects Of 131i Therapy

    The cumulative incidence of hypothyroidism after 131I therapy for hyperthyroidism in patients with Graves’ disease and in patients with toxic nodular goiter. The risk of hypothyroidism in the former group is very high, approaching 100% with long-term follow-up.

    Studies of 131I therapy in nontoxic and/or very large multinodular goiter employing an imaging method for monitoring

    First author, year .

    Are There Permanent Side Effects From The Procedure

    Radioactive iodine is used by doctors as a tracer in diagnosing certain thyroid gland disorders

    It is highly likely that some or most of the thyroid gland will be destroyed with this procedure. Since hormones produced by the thyroid are essential for metabolism, most patients will need to take thyroid pills for the rest of their life following the procedure. Thyroid pills are inexpensive, and patients will typically be instructed to take one per day. There are essentially no other permanent side effects from the procedure.

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    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.

    Vi Modulators Of 131i Therapy

    It has become increasingly clear that a number of factors influence the effect of 131I therapy, whether the indication is hyperthyroidism or a compressive goiter. Despite abundant publicationssome of which are shown in most studies are inadequately designed or have other limitations, i.e., are retrospective, lack a control group, and suffer from selection bias or a too low sample size. However, based on the present knowledge, it seems clear that no single factor reliably predicts the outcome of 131I therapy. In addition, the divergent results between studies may be due to the influence of important confounders not taken into consideration. A number of factors with known or potential influence on 131I therapy are discussed below and shown in . Because these factors probably interact mutually in a complex mannermaking it even more difficult to segregate the impact of each single factorthe need for randomized trials becomes even more imperative.

    Cells, organs, and whole organisms vary in their sensitivity to ionizing radiation due to differences in the cell cycle, intracellular protective systems, and ability to recover. At present, we have little knowledge of this aspect of 131I therapy. A yet unknown factor X might exist that quantitatively mirrors the radiosensitivity of each individual and that could be taken into account when scheduling 131I therapy.

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    Introduction: Thyroid Anatomy And Physiology

    Thyroid gland is the first organ to develop in human embryo. Its development begins 22 days after conception. The thyroid gland develops in the floor of the primitive foregut, between the first and second pharyngeal pouches from the endoderm. It descends to its habitual position, by the anterior neck to the level of the trachea, connecting to the tongues base by the thyroglossal duct. The thyroglossal duct starts from the foramen caecum and normally involutes throughout the development of the embryo when the thyroid occupies its final position in the neck, but sometimes becomes into a pyramidal lobe which is contiguous with the thyroid isthmus .

    The TSHR is a G-protein coupled receptor present in thyroid, lymphocytes, fibroblasts and adipocytes. The binding of TSH to TSHR results in signaling pathway downstream that results in actions of thyroid hormone production .

    Approximately 94% of thyroid hormones are secreted by the thyroid gland as tetraiodothyronine and 6% as triiodothyronine . T4 is catalytically converted to T3 in peripheral tissues by deiodinases enzymes. Both T4 and T3 are mostly bound to carrier thyroxine-binding globulin proteins in the serum .

    Thyroid Disease Symptoms Causes Diagnosis And Treatment Of Thyroid Disease

    Uses of radio isotopes

    What do you know about thyroid disease? Thyroid problems include a number of other disorders that are associated with the thyroid gland. So, what is a thyroid gland? It is a butterfly-shaped gland located in front of the neck. In essence, this gland helps your body use energy and plays a key role in how your body responds to many things. In this article, we will examine thyroid disease from Dr. Salamâs diseases section.

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    Ii The Story Of 131i Therapy

    In 1895, it was discovered that iodine was a constituent of the thyroid gland, and 20 yr later it was demonstrated that the gland could take up iodine actively. In 1923, Henry Plummer introduced iodine as adjunctive treatment to surgery, which was at that time the only treatment for Graves’ disease. Soon thereafter, iodine became an important component in the treatment of Graves’ disease. György Hevesy established, also in 1923, the principle of using radioactive substances to assess biological processes, but further research in that field was limited by the lack of naturally occurring radioactive substances. A breakthrough came in 1934 when Enrico Fermi described the artificial production of 22 new radioactive elements, among these iodine isotopes, by irradiating aluminum foil with an -emitting source.

    What Is Radioiodine Therapy And How Is It Used

    Radioactive Iodine I-131 therapy is a treatment for an overactive thyroid, a condition called hyperthyroidism. Hyperthyroidism can be caused by Graves’ disease, in which the entire thyroid gland is overactive, or by nodules within the gland which are locally overactive in producing too much thyroid hormone.

    Nuclear medicine uses small amounts of radioactive material called radiotracers. Doctors use nuclear medicine to diagnose, evaluate, and treat various diseases. These include cancer, heart disease, gastrointestinal, endocrine, or neurological disorders, and other conditions. Nuclear medicine exams pinpoint molecular activity. This gives them the potential to find disease in its earliest stages. They can also show whether you are responding to treatment.

    The thyroid is a gland in the neck that produces two hormones that regulate all aspects of the body’s metabolism, the chemical process of converting food into energy. When a thyroid gland is overactive, it produces too much of these hormones, accelerating the metabolism.

    Radioactive iodine , an isotope of iodine that emits radiation, is used for medical purposes. When a small dose of I-131 is swallowed, it is absorbed into the bloodstream in the gastrointestinal tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland’s cells.

    Radioactive iodine I-131 may also be used to treat thyroid cancer.

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    E Severity Of Disease

    The severity of hyperthyroid diseases can be assessed in several ways, and the most adequate definition of disease severity is a matter for discussion. From a clinical point of view, the thyroid hormone levels seem to be relevant markers of disease activity/severity due to their correlation with the symptoms of hyperthyroidism. However, it could be argued that for monitoring Graves’ disease, indicators of the autoimmune statuslike the serum level of TRAb, the presence of TAO, and the size of the thyroid glandcould be just as relevant to monitor. Use of ATD is an important confounder in this context, particularly because the dose of ATD needed to obtain euthyroidism parallels the disease severity. Although the impact of external factors, like ATD or other kinds of intervention, can relatively easily be investigated by randomized trials, it is much more difficult to explore the impact of the intrinsic features of the disease. Usually, regression analyses are used to segregate any independent effect of disease severity from a range of other factors that might affect the outcome of 131I therapy. Post hoc regression analyses have their limitation, and this is probably one of the main reasons for the conflicting findings.

    V Adverse Effects Of 131i Therapy

    Radioactive Iodine Ablation to Treat Thyroid Disease: Pediatric Thyroid Center at CHOP (6 of 9)

    A few studies have evaluated the overall risk of 131I therapy. Franklyn et al. found an increased mortality among 7209 hyperthyroid patients treated with 131I between 1950 and 1989. The excess mortalityrelated to thyroid, cardiovascular, and cerebrovascular diseases, and fractures of the femurwas most evident in the first year after therapy and declined thereafter. In a population-based study of 2668 individuals aged 40 yr or older treated between 1984 and 2002, the same group reported that 131I therapy was associated with an increased mortality, mostly due to cardiovascular diseases . Interestingly, the mortality was not increased among patients receiving levothyroxine therapy for 131I-induced hypothyroidism . Studies by Metso et al. demonstrated that the rates of death and vascular diseases were increased by 12%, and the risks remained elevated 35 yr after the 131I therapy. However, it is very difficult to make any conclusion on causality from population-based studies because any increased risk associated with 131I therapy may be caused by the hyperthyroid disorder rather than the treatment . It needs further clarification by well-controlled studies whether 131I therapy per se causes excess morbidity and mortality.

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    What Is Radioactive Iodine

    Iodine, in the form of iodide, is made into two radioactive forms of iodine that are commonly used in patients with thyroid diseases: I-123 and I-131 . The radiation emitted by each of these forms of iodine can be detected from outside the patient to gain information about thyroid function and take pictures of the size and location of thyroid tissues. RAI is safe to use in individuals who have had allergic reactions to seafood or X-ray contrast agents, since the reaction is to the compound containing iodine, not the iodine itself. RAI is given by mouth in pill or liquid form.

    Thyroid Disease And How The Thyroid Gland Works

    Simply put, the thyroid gland produces hormones that are needed for your body to function normally. Thyroxine is a hormone produced by the thyroid gland, and a small part of it is produced called triiodothyronine, which keeps you active all day. Basically, this hormone strengthens your bodyâs energy.

    The thyroid gland is usually regulated by the brain. In fact, there is a strong connection between your brain and your thyroid gland. When thyroid levels are low, your brain produces a hormone called thyrotropin. Sometimes, the thyroid tends to produce extra hormones, and this can be classified as hyperthyroidism because your thyroid is overactive and overproduces hormones.

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    How Is The Procedure Performed

    Treatment for hyperthyroidism is almost always done on an outpatient basis because the dose required is relatively small.

    The radioiodine I-131 is swallowed in a single dose, in capsule or liquid form, and is quickly absorbed into the bloodstream in the gastrointestinal tract and concentrated from the blood by the thyroid gland, where it begins destroying the gland’s cells. Although the radioactivity from this treatment remains in the thyroid for some time, it is greatly diminished within a few days. The effect of this treatment on the thyroid gland usually takes between one and three months to develop, with maximum benefit occurring three to six months after treatment. Usually, a single dose is successful in treating hyperthyroidism. However, rarely, a second treatment is needed, and very rarely a third treatment may be needed.


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