**6. Patient preparation**

Certain evaluations for adequate treatment include the treatment history such as ATDs, food or medication containing iodine that blocked radioiodine uptake that needs to discontinue before the treatment, and the duration of their period as shown in **Table 1**.


#### **Table 1.**

*Pharmaceuticals containing iodine block of RAI uptake [4, 6, 11, 23, 25].*

#### **Figure 3.**

*Scintigraphy thyroid showed enlargement of both thyroid lobes, with high diffuse uptake of a Tc-99 m pertechnetate.*

The patient should also be advised to avoid meals for at least 2 hours before and 2 hours after the oral administration of RAI. Large meals can slow the absorption of RAI. Laboratory results, including free T4, free T3, Thyroid-stimulating hormone (TSH). Thyroid scintigraphy is used to assess the potential variability distribution of RAI in the thyroid gland. Graves' Disease scintigraphy pattern is a diffuse high uptake at the thyroid gland. It can differentiate between Graves' Disease with toxic adenoma and toxic multinodular goiter, as shown in **Figure 3**. Ultrasonography assessment may be useful if patients have a contraindication for the scintigraphy, such as during breastfeeding and pregnancy [6]. The choice of testing depends on cost, local availability, and expertise. RAIU measurements are not required when fixed activities are used. Thyroid ultrasonography can be used to determine thyroid volume. Pregnancy test for child-bearing females within 72 hours before the RAI administration, and when pregnancy is excluded, the test can be omitted.

For patients with ophthalmopathy, RAI can exacerbate existing Graves' ophthalmopathy (GO) [11, 12, 23]. Smokers, high serum triiodothyronine pre-treatment, posttherapy hypothyroidism, and thyroid-stimulating receptor antibody are also associated with an increased risk of developing or worsening ophthalmopathy [23]. Steroids prevent the risk of RAI-induced ophthalmopathy without influence the outcome of therapy. Mild and active ophthalmopathy pre-exists patients with highrisk factors associated with development or worsening of ophthalmopathy should receive steroid prophylaxis [25, 27, 28].

RAI therapy may need to be repeated. Patients also need a long-term follow- up because of the likelihood of eventual hypothyroidism and very uncommon side effects. Written information must be provided, and the patient should obtain written informed consent before therapy.

#### **7. Contraindication**

Absolute contraindications of RAI are in pregnancy and during breastfeeding and in patients who cannot comply with radiation safety regulations. Relative contraindications are uncontrolled hyperthyroidism and active thyroid orbitopathy (especially in smokers) [4, 6, 12, 25]. RAI is not contraindicated in large goiters, even if partially retrosternal or intrathoracic [25]. A higher cure rate reaches up to 96%, even for thyroid size of more than 40 gram [12].
