**8. Special situations in nuclear medicine and radiation protection**

## **8.1. Pregnancy and breastfeeding**

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,

Radiobiology studies the effects of ionizing radiation on cells. These effects are diverse and

• Depending on its action on cells: direct effects on DNA (breakage of DNA strands) or indi-

• From a point of view of dose dependence: deterministic effects ("dose-dependent", which can be prevented if this dose threshold is not exceeded) and stochastic effects (due to

The main objective of radiation protection is to prevent the appearance of deterministic effects and limit the possibility of stochastic effects. The pillars of radiological protection are based

• Justification: obtain positive net benefit. Benefit/risk balance, where the benefit of the test

• Optimization: exposure to ionizing radiation should be as low as reasonably achievable *("ALARA principle")*. It is because of that calculated-dose method may be more acceptable, due to considering that principle and an increasing desire for lowering annual dose of the

• Limitation of doses: use the lowest possible dose to obtain good image quality and limit the radiological tests to be performed. Maximum doses (mSv) are established for members of the public, caregivers of the patient and health personnel, as well as specifically for the

• Time: the shorter the time in contact with the radiation source (patient), the lower the re-

• Distance: it must be as far as possible from the radiation source (patient), since the dose received will be lower. The physical law of the *"inverse of the square of the distance"* is applied in such a way that if we move away twice the distance of the patient, we will decrease the dose 1/22 (1/4); if we go three times, the received dose will decrease 1/33 (1/9), and so on. • Shielding: separation between the issuing source (patient) and the rest of people (operators / public). There are "primary shields" such as lead tubes used as a protector for the injection of the radiotracer. Also, mention the existence of "secondary shields", such as leaded aprons, thyroid protectors, eye protectors for lenses, gloves, glass or special screens.

chance, cannot be prevented since they do not present dose threshold).

saliva, sweat, urine, feces, genital fluids or breastfeeding.

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

**7.2. Objective, pillars and radiological protection measures**

rect effects (cellular damage by free radicals).

are classified into three large groups:

must be greater than the risk.

general population [17].

lens, skin and limbs.

ceived dose.

The general measures in radiological protection are:

on:

42 Thyroid Disorders

*"In nuclear medicine, a woman of childbearing age is considered pregnant until proven otherwise".* In the nuclear medicine services, there are visible information leaflets to the public, especially for women of childbearing age who may be pregnant and whose duty it is to inform the center's health personnel.

In addition, it is mandatory to ask the date of last menstruation and about the possibility of pregnancy in the clinical history. Also, all women in this age group who are to be treated with radionuclides of iodine must have a negative pregnancy test, prior to the administration of the radiopharmaceutical as therapy [16]. The result of the pregnancy test will be recorded in the patient's health history.

Pregnant women with untreated overt hyperthyroidism are at increased risk for spontaneous miscarriage, congestive heart failure, thyroid storm, preterm birth, pre-eclampsia, fetal growth restriction, and increased perinatal morbidity and mortality [9].

Regarding the use of radioiodine, fertility could be reduced and abnormalities offspring will be increased. Several studies are related to larger doses of 131I that are used to treat thyroid cancer [16]. Medical personnel should warn patients to avoid becoming pregnant during the time following the procedure with radionuclides. The time required depends on the type of radiopharmaceutical used; in the case of 131I (either used for the treatment of hyperthyroidism or as ablative therapy of possible thyroid remnants in differentiated thyroid carcinoma) the consensus is that the conception should be deferred for 12 weeks (minimum 6 months) and that maternal thyroid function should be normal [16].

By avoiding pregnancy during this period, the objective is achieved to reduce the probability that the dose received to an embryo or fetus is greater than 1 mSv (dose limit to the public). Keep in mind that these compounds cross the placental barrier and there is a risk of an exposure of the fetus that can reduce the intelligence quotient by 30 points per gray (100 rads), and may be associated with attention deficit disorders and impairment of figurative memory in the offspring and also a slightly increased cancer-risk possibility. According on the gestation period the patient is in, there is a greater probability of risk of [3, 16]:

patients should undergo dialysis in a private room and monitored by radiophysics personnel.

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

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

45

All authors have read and approved the manuscript and affirm that the requirements for

The authors declare that the protocols established by their respective health centers have been followed to access the data of the clinical histories in order to be able to carry out this type of

For the treatment of your illness, we have given you a radioactive substance called 131-Iodine. This substance will remain in your body for several days until it disappears completely through the urine, because it eliminates itself. While this is beneficial for you, certain precautions must be taken in order to protect the people with whom you live. Therefore, we recommend that

• If you stay in a room with your family for a long time, try to be as far away from them as

you follow these instructions for the next 7–10 days (from xx-xx-xxxx to xx-xx-xxxx):

• Avoid being around pregnant women and young children.

publication with the purpose of research/dissemination for the scientific community.

This work did not receive funding for any aspect of compilation or publication.

Apart from this, no additional precaution is needed.

1. Design and conception of the manuscript: Elena Espinosa Muñoz.

4. Drafting, revision, approval of the manuscript: Elena Espinosa Muñoz.

3. Analysis and interpretation of data: Elena Espinosa Muñoz.

The authors declare that they have no conflict of interest.

**Acknowledgements**

authorship have been met:

**Conflict of interest**

**A. Appendix 1**

Name and surname:

Dear SR / SRA:

**Nuclear medicine service.**

**Patients in radioiodine treatment.**

possible (at least 1 meter away).

Regional university hospital of Málaga.

2. Data collection: Elena Espinosa Muñoz.


For these reasons, radioiodine therapy is contraindicated in pregnancy, being the pharmacological treatment with oral antithyroid drugs the first line of therapy, mainly with propylthiouracil. Radioiodine would be acceptable when pregnancy is contemplated after at least 6 months, and thyroidectomy if conception is envisaged within a 6 month interval and/or if there is a large goiter [3]. It must also be borne in mind that these possibilities of therapy are considered second line, in the case of contraindication, refractoriness or failure to adherence to pharmacological therapy with anti-thyroid drugs.

Regarding breastfeeding, there are general guidelines on the time of interruption depending on the radiopharmaceutical used. In the case of <sup>131</sup>I for therapeutic purposes, breastfeeding should be completely suppressed after administration of 131I. This condition does not occur with antithyroid drugs, since studies have shown that only limited amounts of propylthiouracil or carbimazole are secreted in breast milk, which explains that the neonatal exposure to these drugs is insignificant. Therefore, the use of low-moderate doses of carbimazole (<20 mg) or propylthiouracil (<300 mg) during breastfeeding is recommended [3].

#### **8.2. Chronic renal failure and dialysis**

Patients with chronic renal failure do not have a contraindication to receive treatment with 131-Iodine.

Holst et al. reviewed the medical literature and concluded that the 131I dose does not need to be adjusted in patients who have end-stage renal disease and who are referred for the therapy of hyperthyroidism. However, they recommended 131I administration as soon as possible after dialysis and a delay in subsequent dialysis until the maximum 131I uptake has occurred in the thyroid [16].

Some cases of contamination of dialysis machines have been reported. In these cases where there may be a slight contamination with 131-Iodine in disposable items such as syringes or waste bags, these can be stored for several half-life periods until activity declines. Also these patients should undergo dialysis in a private room and monitored by radiophysics personnel. Apart from this, no additional precaution is needed.
