**6.1. Different therapeutic options in hyperthyroidism**

**Figure 3.** Hyperfunctioning nodulation is seen at the base of the right thyroid lobe. *Courtesy of H.R.U. Málaga, Spain.* 

**Figure 4.** We can see the existence of a large hyperfunctioning nodulation that occupies the left thyroid lobe. *Courtesy of* 

*Nuclear Medicine Department.*

38 Thyroid Disorders

*H.R.U. Málaga., Spain. Nuclear Medicine Department.*

Current therapeutic options for these pathologies include antithyroid drugs (ATD), radioactive iodine and thyroidectomy. The choice of treatment depends on the type of pathology (*Graves' disease*, toxic multinodular goiter, pretoxic or toxic adenoma), physiological characteristics of the patient (age, pregnancy, breastfeeding), co-morbidities (advanced age, heart failure, large compressive intrathoracic goiters, thyroid ophthalmopathy), as well as refractoriness to the treatment administered [8, 14].

Antithyroid drugs (ATD) therapy is usually recommended as the initial treatment for hyperthyroidism (especially in *Graves' disease*), achieving normalization of thyroid function in 4–6 weeks [8].

There are several antithyroid drugs, the most used in our environment are methimazole and propylthiouracil. For several reasons, propylthiouracil is preferred during pregnancy. Avoidance of the use of propylthiouracil (PTU) was recently recommended in childhood because of the high risk of PTU-induced hepatitis. Because methimazole (active metabolite of carbimazole) has a longer half-life and is effective as a single daily dose, it is particularly helpful in younger children. Daily loading doses of 10–30 mg of methimazole or 100–300 mg of propylthiouracil are appropriate for most patients [15, 16].

The medication is prescribed for 12–18 months normally, with the aim of achieving remission of the disease. However, the frequency of recurrences (more frequently in young males) and severe side effects like cytopenias, vasculitis, liver failure or agranulocytosis (higher in pediatric patients than adults) are a main limitation of ATD treatment [8, 14, 16].

Radioiodine therapy and surgery are usually the second-line treatments in *Graves' disease*. It does not happen in the case of toxic nodular goiter (toxic multinodular goiter and toxic adenoma), where definite and effective treatment can be achieved only with radioiodine or surgery [13]. So, both are considered as the first line of treatment for these pathologies and not the second line as in *Graves' disease* [17].

The use of 131-Iodine in the treatment of hyperthyroidism is increasing, as it is easy to administer, relatively inexpensive, safe and highly effective with a cure rate approaching 100% after one or more activity [18].

In our department, we administer single doses of radioiodine, which are prepared in individual capsules to be taken orally. The said capsules are specifically detailed with the data of the patient who is going to receive the metabolic treatment, as well as the amount of dose that the capsule carries. That way, it is possible to reduce failures in the administration of doses between patients.

goiters, multinodular goiters, large nodules on thyroid or refuse treatment with 131-Iodine. Although the treatment rate is high with surgery, serious complications such as recurrent

Nuclear Medicine in the Assessment of Thyrotoxicosis Associated with Increased Thyroid…

http://dx.doi.org/10.5772/intechopen.77161

41

In all cases of treatment with 131-Iodine (*Graves' disease*, pretoxic/toxic multinodular goiter or pretoxic/toxic adenoma), treatment is performed in our department on an outpatient basis if

Prior to the administration of the radioiodine dose, metabolic treatment is explained, as well as all the radiological protection measures to be followed, possible side effects such us fever due to radiation-thyroiditis (which usually remits at 48 h); cervical/pharyngeal complaints, that usually remit with analgesics or tachycardia. Additional treatment with β-blockers (except in patients with asthma or cardiac failure) during the first 2 weeks of management may help to reduce the patient's symptoms. This treatment can be given orally twice daily, at a dose of 2 mg/kg/day, and stopped when the patient becomes euthyroid [15]. After a detailed explanation, informed consent is signed. If there are women of childbearing age, it is mandatory to ask the date of last menstruation and request pregnancy tests. To receive a therapeutic dose of 131I, it is also necessary to have a

As for the preparation, the patient should come fasting for at least 4 h and have stopped the medication with antithyroid drugs 2 days before. The medication with antithyroid drugs will be reintroduced 72 h after taking the radioiodine and half the dose scheduled until the next revision by endocrinology. There is another option such as discontinuing antithyroid drugs 1

Once the patient has ingested the capsule, it is not necessary to carry out any diet low in iodine. However, it is mandatory that the patient stays for 2 more h fasting and performs the radiological protection measures (already explained previously) for 7–10 days following the

Following treatment, patients must be evaluated at 1, 3, 6 and 12 months for thyroid function tests, clinical symptoms and physical examination by endocrinology physicians to observe the response to metabolic therapy. Patients who develop euthyroidism and hypothyroidism

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,

administration of 131I. This is due to a reasonable 131-Iodine half-life of 8 days [8, 13].

**7. Radiation protection: ionizing radiation and radiobiology.** 

**Objective, pillars and radiological protection measures**

laryngeal nerve injury and hypoparathyroidism may be seen [8, 13].

week before treatment and starting again 1 week after treatment [13].

**6.2. Radioiodine (131I) administration protocol in our center**

the dose of 131I is less than 30 mCi (1110 MBq).

thyroid scintigraphy in the last year.

in the sixth month are accepted as cured [13].

**7.1. Ionizing radiation and radiobiology**

There is no consensus regarding the optimum dose of radioiodine [17]. There are fixed doses regimens of 10 mCi (370 MBq) generally used to treat *Graves 'disease*, in addition to capsules with a dose of 12 mCi (444 MBq) at 15 mCi (555 MBq), for cases of pretoxic and toxic multinodular goiter and adenoma, respectively. Also, calculated-dose strategies (doses adjusted to patient's weight) can be used, which is considered the most specific option, since the patient is prevented from receiving a higher or lower dose than necessary. In a study conducted by Rokni H et al., it was observed that, interestingly, permanent hypothyroidism was not significantly different between calculated and fixed dose regimens [17].

Once the dose of 131I is administered, the patient may present three situations. The goal of treatment of hyperthyroidism is to bring patients to the euthyroid state.

Hypothyroidism is recognized as an important and more frequent side effect of treatment for hyperthyroidism. Hypothyroidism may be transient (usually 2–4 months after therapy) or permanent [17, 18]. Patients with permanent hypothyroidism usually need additional treatment with thyroid hormones (levothyroxine), whose doses are increased or decreased according to clinical and analytical controls.

On the other hand, it may happen that once the dose of 131-Iodine is administered, the patient persists in hyperthyroidism. In this case, refractoriness is discussed at the initial dose of metabolic therapy and it may be necessary to administer a second dose of 131I after 6 months from the initial dose.

Risk factors such as the presence of thyroid antibodies, age and sex of the patient, etiology of hyperthyroidism, administration of antithyroid drugs and goiter size can influence the outcome of 131I treatment [18]. Patients with antithyroid antibodies, young males, *Graves' disease* (more frequent than multinodular goiter and pretoxic/toxic adenoma), long period of time with high doses of antithyroid drugs or relapse after its suspension, large intrathoracic compressive goiters or *Graves ´ophthalmopathy*, have more risk of failure to the initial treatment with 131-Iodine.

These fixed dose regimens of 131-Iodine (<sup>131</sup>I) for each pathology: 10 mCi [370 MBq] *(Graves' disease)*, 12 mCi [444 MBq] (multinodular goiter and adenoma in "pre-toxic situation"), 15 mCi [555 MBq] (toxic multinodular goiter and toxic adenoma) have been previously studied, increasing the probability of healing and providing the lowest possible radiation to the rest of the body. Calculated-dose strategies (doses adjusted to patient's weight) have the advantage that they are individualized for each patient. In our department, calculated-dose strategies are used in childhood and adolescent patients, as well as in adults of low weight. However, the optimal way is to use adjusted doses to the weight of the patient and to a lesser extent the fixed doses.

Surgery (total thyroidectomy) is recommended when there are side effects of antithyroid drugs, non-adherence to pharmacological treatment, non-remissions in hyperthyroidism's recurrences after prolonged medical treatment, patients with severe exophthalmos, very large goiters, multinodular goiters, large nodules on thyroid or refuse treatment with 131-Iodine. Although the treatment rate is high with surgery, serious complications such as recurrent laryngeal nerve injury and hypoparathyroidism may be seen [8, 13].

## **6.2. Radioiodine (131I) administration protocol in our center**

In our department, we administer single doses of radioiodine, which are prepared in individual capsules to be taken orally. The said capsules are specifically detailed with the data of the patient who is going to receive the metabolic treatment, as well as the amount of dose that the capsule carries. That way, it is possible to reduce failures in the administration of doses

There is no consensus regarding the optimum dose of radioiodine [17]. There are fixed doses regimens of 10 mCi (370 MBq) generally used to treat *Graves 'disease*, in addition to capsules with a dose of 12 mCi (444 MBq) at 15 mCi (555 MBq), for cases of pretoxic and toxic multinodular goiter and adenoma, respectively. Also, calculated-dose strategies (doses adjusted to patient's weight) can be used, which is considered the most specific option, since the patient is prevented from receiving a higher or lower dose than necessary. In a study conducted by Rokni H et al., it was observed that, interestingly, permanent hypothyroidism was not signifi-

Once the dose of 131I is administered, the patient may present three situations. The goal of

Hypothyroidism is recognized as an important and more frequent side effect of treatment for hyperthyroidism. Hypothyroidism may be transient (usually 2–4 months after therapy) or permanent [17, 18]. Patients with permanent hypothyroidism usually need additional treatment with thyroid hormones (levothyroxine), whose doses are increased or decreased accord-

On the other hand, it may happen that once the dose of 131-Iodine is administered, the patient persists in hyperthyroidism. In this case, refractoriness is discussed at the initial dose of metabolic therapy and it may be necessary to administer a second dose of 131I after 6 months from

Risk factors such as the presence of thyroid antibodies, age and sex of the patient, etiology of hyperthyroidism, administration of antithyroid drugs and goiter size can influence the outcome of 131I treatment [18]. Patients with antithyroid antibodies, young males, *Graves' disease* (more frequent than multinodular goiter and pretoxic/toxic adenoma), long period of time with high doses of antithyroid drugs or relapse after its suspension, large intrathoracic compressive goiters or *Graves ´ophthalmopathy*, have more risk of failure to the initial treatment with 131-Iodine. These fixed dose regimens of 131-Iodine (<sup>131</sup>I) for each pathology: 10 mCi [370 MBq] *(Graves' disease)*, 12 mCi [444 MBq] (multinodular goiter and adenoma in "pre-toxic situation"), 15 mCi [555 MBq] (toxic multinodular goiter and toxic adenoma) have been previously studied, increasing the probability of healing and providing the lowest possible radiation to the rest of the body. Calculated-dose strategies (doses adjusted to patient's weight) have the advantage that they are individualized for each patient. In our department, calculated-dose strategies are used in childhood and adolescent patients, as well as in adults of low weight. However, the optimal way is

to use adjusted doses to the weight of the patient and to a lesser extent the fixed doses.

Surgery (total thyroidectomy) is recommended when there are side effects of antithyroid drugs, non-adherence to pharmacological treatment, non-remissions in hyperthyroidism's recurrences after prolonged medical treatment, patients with severe exophthalmos, very large

cantly different between calculated and fixed dose regimens [17].

ing to clinical and analytical controls.

the initial dose.

treatment of hyperthyroidism is to bring patients to the euthyroid state.

between patients.

40 Thyroid Disorders

In all cases of treatment with 131-Iodine (*Graves' disease*, pretoxic/toxic multinodular goiter or pretoxic/toxic adenoma), treatment is performed in our department on an outpatient basis if the dose of 131I is less than 30 mCi (1110 MBq).

Prior to the administration of the radioiodine dose, metabolic treatment is explained, as well as all the radiological protection measures to be followed, possible side effects such us fever due to radiation-thyroiditis (which usually remits at 48 h); cervical/pharyngeal complaints, that usually remit with analgesics or tachycardia. Additional treatment with β-blockers (except in patients with asthma or cardiac failure) during the first 2 weeks of management may help to reduce the patient's symptoms. This treatment can be given orally twice daily, at a dose of 2 mg/kg/day, and stopped when the patient becomes euthyroid [15]. After a detailed explanation, informed consent is signed.

If there are women of childbearing age, it is mandatory to ask the date of last menstruation and request pregnancy tests. To receive a therapeutic dose of 131I, it is also necessary to have a thyroid scintigraphy in the last year.

As for the preparation, the patient should come fasting for at least 4 h and have stopped the medication with antithyroid drugs 2 days before. The medication with antithyroid drugs will be reintroduced 72 h after taking the radioiodine and half the dose scheduled until the next revision by endocrinology. There is another option such as discontinuing antithyroid drugs 1 week before treatment and starting again 1 week after treatment [13].

Once the patient has ingested the capsule, it is not necessary to carry out any diet low in iodine. However, it is mandatory that the patient stays for 2 more h fasting and performs the radiological protection measures (already explained previously) for 7–10 days following the administration of 131I. This is due to a reasonable 131-Iodine half-life of 8 days [8, 13].

Following treatment, patients must be evaluated at 1, 3, 6 and 12 months for thyroid function tests, clinical symptoms and physical examination by endocrinology physicians to observe the response to metabolic therapy. Patients who develop euthyroidism and hypothyroidism in the sixth month are accepted as cured [13].
