I-131 Radioiodine Therapy is a therapy that is mostly used in the treatment of differentiated thyroid cancers, i.e., papillary carcinoma and follicular carcinoma. It tends to be applied during thyroidectomy (removal of the thyroid gland ), and this is performed after surgery.

The thyroid gland is known to take iodine naturally to produce thyroid hormones. This biological property is employed in radioiodine therapy, where radioiodine (I-131) is selectively taken into the residual thyroid tissues and thyroid cancer cells (and also metastatic deposits).

The therapeutic dosage varies depending on the clinical intent: remnant ablation, adjuvant therapy, or treatment of metastatic disease. The intermediate-risk patients, or those having a possible residual or minimal metastatic disease, usually have a dose of 150 mCi (millicurie). The treatment helps to reduce the recurrence and helps to follow-up the disease long-term.

How does I-131 work?

Iodine-131 refers to a radioactive isotope, which is a beta emitter and is used as a radioiodine treatment. This radiation kills the thyroid tissue as well as the cancer cells by damaging the DNA.

The I-131 can be given orally (in the form of a capsule) or administered as a liquid, after which it circulates in the blood and is actively distributed to the thyroid cells with the help of the sodium-iodide symporter. This treatment provides the thyroid with a very precise dose of radiation because the majority of other body tissues cannot absorb iodine as well as the thyroid and thus lowers the amount of radiation to non-thyroid tissues.

Indications for I-131 Radioiodine Therapy – 150 mCi

This dose is normally denoted in the following ways:

• The ablation of remnant thyroid tissue after thyroidectomy.
• Involvement of the regional lymph nodes management.
• Metastases (distant) (e.g., lungs) are few.
• Weakly-differentiated thyroid carcinoma.
• High-level T 4 of thyroglobulin and no disease appearance upon imaging.
• High-grade residual disease adjuvant therapy.

The therapy also reduces the recurrence rates as it eliminates the remaining thyroid tissue, which, in turn, enhances the precision of the thyroglobulin monitoring and a resultant whole-body scan.

Preparation for I-131 Radioiodine Therapy

To achieve the best efficacy of treatment, it should be prepared:

1. Elevation of TSH Levels

The level of TSH is supposed to be higher than 30 mIU/L to have the best absorption of iodine.

Methods:

a. Thyroid Hormone Withdrawal

• Discontinuation of thyroid hormone replacement (e.g., Thyronorm, Eltroxin) within 3-6 weeks.
• Such causes hypothyroidism, an increase in TSH levels above the normal level.
• Possible symptoms: fatigue, weight gain, depression, constipation, cold intolerance

b. Recombinant Human TSH (rhTSH – Thyrogen®)

• Given in two-day injections.
• Allows the use of treatment using thyroid hormone.
• Avoids hypothyroid symptoms
• Perhaps more expensive or unavailable.

These two methods are both desirable, but a choice and clinical discretion issue.

2. Low-Iodine Diet

• Follow for 1-2 weeks before therapy.
• Enhances the uptake of I-131 by reducing the stores of iodine.
• Avoid: dairy products, eggs, salt that is iodized, seafood, and some food dyes.

3. Baseline Tests and Imaging

The following might be required before the therapy:

• Serum thyroglobulin and anti-thyroglobulin levels of antibodies.
• Free T4 and TSH concentrations.
• Neck ultrasound
• Diagnostic whole body Iodine scan (where necessary)

Procedure: What to Expect

• The dosage amount (150 mCi) is taken orally (capsule or liquid).
• At least 2 hours of fasting: It is required both before and after administration.
• Temporary isolation can be required based on the radiation safety guidelines.

Post-Therapy Instructions & Isolation Guidelines

I-131 is excreted in urine, saliva, sweat, and feces; thus, there are radiation precautions:

• Physical separation from other individuals, children, and expectant women (3-7 days)
• Use another bathroom where possible.
• Flush twice following the toilet.
• Clean your hands regularly.
• Spend some time apart for a couple of days.
• Stay out of public and workplaces.
• Avoid getting pregnant within 6 months of treatment.

Possible Side Effects

The radioiodine treatment is generally extremely tolerable, with some patients exhibiting:

• Swelling or pain of neck.
• Tasting dysfunction or dry mouth.
• Nausea or fatigue
• Temporary menstrual irregularities
• Infrequently, low blood cell count or fertility (with repeated high doses)

The side effects are predominantly mild and temporary.

Follow-Up After Therapy

Post-Therapy Scan

• Performed 5-7 days of treatment.
• Monitors the iodine consumption and cure.

Long-Term Monitoring

• Regular blood test (TSH, thyroglobulin, anti- Tg antibodies).
• Regular imaging as required.
• TSH-suppressing thyroid hormone.

Conclusion

The I-131 Radioiodine Therapy (150 mcI) plays a critical role in the total management of the differentiated thyroid cancer following thyroidectomy. It selectively destroys residual thyroid tissue and cancer tissue, reduces recurrent opportunities, and provides better long-term follow-up.

With appropriate usage, following of the radiation safety rules, and thorough follow-ups, this treatment can be safe and efficient, and besides the enhanced control of the disease, the patient has an opportunity to enjoy a longer life.

Reporting: Not Applicable