I-131 Radioiodine Therapy – 30 mCi

I-131 Radioiodine Therapy – 30 mCi is a form of nuclear medicine therapy to remove the remaining thyroid tissue in patients with other thyroid conditions treated with thyroid surgery (e.g., papillary, follicular thyroid cancer). At Molecular Diagnostics and Therapy, Dr. Nikunj Jain, Co-Founder and HOD – Nuclear Medicine, provides expert guidance for patient selection and radioiodine treatment planning. Even though the thyroid has been removed, there may be small amounts of thyroid tissue or small cancer cells remaining.

Radioiodine given in a low dose kills the rest of the tissue, lowers the chances of cancer returning, and makes follow-up easier as well. The thyroid is typically able to take up the iodine in the blood and make thyroid hormones. Similarly, radioiodine also acts in this way, with the iodine being taken up by the remaining cells of the thyroid. The cells become radioactive and absorb radiation, causing their destruction, but not the destruction of most other tissues. The low-dose treatment is a 30 mCi dose and is typically used when small amounts of thyroid tissue are removed in a patient who is at low risk. Alternatively, it is usually given without hospitalisation.

What is Radioiodine Therapy?

Radioiodine therapy is a procedure in which a small amount of radioactive iodine is used to kill any remaining thyroid tissue or any cancer cells. This therapy assists with the following:

• Ablate residual thyroid following thyroidectomy.

• Destroy minute cancer cells that may still be present.

• Enhance follow-up tests, including thyroglobulin blood tests.

• Enhance the usefulness of scans in the future.

• Minimize the likelihood of recurrence of cancer.

A 30 mCi dose is generally recommended for patients with low-risk thyroid cancer, especially if imaging does not show that the lymph nodes and distant spread of the thyroid cancer are considered low risk.

Why is the 30 mCi Dose Used?

A dose of 30 mCi is given to certain patients to destroy remnants of the thyroid gland. May be recommended if:

• The patient has a small amount of residual thyroid tissue following near-complete thyroidectomy.

• It is a low-risk cancer and shows no evidence of disease on scans.

• The physician desires that the patient be prepared to undergo extensive surveillance using thyroglobulin.

• There is very limited thyroid tissue remaining.

• The physician believes that the low dosage suffices.

A 30 mCi dose works well, like high doses, to remove the tissue, but keeps radiation and side effects low.

Preparation Before I-131 Therapy (30 mCi)

The therapy should be properly prepared. Raising the TSH level and following a low-iodine diet are two important steps.

1. Elevation of TSH (Thyroid Stimulating Hormone)

For radioiodine to be effectively absorbed by residual thyroid cells, TSH levels should typically be above 30 mIU/L. TSH elevation stimulates thyroid tissue to absorb iodine more efficiently. Two methods are used to achieve this.

Thyroid Hormone Withdrawal

Patients stop taking thyroid hormone replacement medication (such as levothyroxine) for 3–4 weeks before therapy. This causes TSH levels to rise naturally due to temporary hypothyroidism. Possible symptoms during withdrawal may include:

• Fatigue

• Weight gain

• Cold intolerance

• Constipation

• Low mood

• Menstrual irregularities

These symptoms are temporary and resolve once hormone therapy is restarted.

Recombinant Human TSH (rhTSH – Thyrogen®)

Another option is rhTSH injections, given over two consecutive days before therapy. Benefits include:

• Patients can continue taking thyroid hormone medication.

• Avoids symptoms of hypothyroidism.

• More convenient for elderly patients or those with other medical conditions.

Your doctor decides the most suitable preparation method.

2. Low-Iodine Diet

A low-iodine diet for 1–2 weeks before treatment helps reduce iodine levels in the body, improving the uptake of radioactive iodine by the remaining thyroid cells.

Foods to Avoid

• Iodized salt or sea salt

• Dairy products (milk, cheese, yogurt)

• Seafood (fish, shrimp, seaweed)

• Egg yolks

• Soy products

• Processed foods containing iodized salt

• Foods with red food dye (may contain iodine)

Foods Allowed

• Fresh fruits and vegetables

• Egg whites

• Non-iodized salt

• Fresh, unprocessed meat and poultry

• Plain rice, pasta, and homemade bread without iodized salt

How is I-131 Radioiodine Therapy (30 mCi) Administered?

The therapy is usually given orally in the form of a capsule or liquid solution. Key points include:

• Patients may need to fast for about 4 hours before and after the dose.

• The treatment is generally performed on an outpatient basis.

• A short observation period may be required after administration.

After receiving the dose, the radioactive iodine travels through the bloodstream and is absorbed by the remaining thyroid cells.

Post-Therapy Safety Instructions

Although the radiation dose is relatively low, some precautions are recommended for 3 days to 2 weeks after therapy to reduce radiation exposure to others. Patients may be advised to:

• Maintain distance from children and pregnant women.

• Sleep separately from others for a few days.

• Use a separate bathroom if possible.

• Flush the toilet twice after use.

• Avoid kissing or close physical contact.

• Avoid sharing utensils or food.

• Wash your hands frequently and maintain good hygiene.

• Drink plenty of fluids to help eliminate radioactive iodine from the body.

Your nuclear medicine team provides detailed written instructions specific to your situation.

Follow-Up After 30 mCi Therapy

A post-therapy whole-body scan may be performed 3–7 days after treatment to:

• Confirm iodine uptake in residual thyroid tissue.

• Detect any unexpected areas of iodine uptake.

• Evaluate the effectiveness of the ablation.

Long-term follow-up may include:

• Blood tests for serum thyroglobulin levels.

• Neck ultrasound.

• Periodic diagnostic scans if needed.

• Adjustment of thyroid hormone replacement dosage.

Benefits of Low-Dose I-131 Therapy (30 mCi)

• Effective for low-risk differentiated thyroid cancer.

• Targeted treatment with minimal effect on other tissues.

• Lower radiation exposure compared to higher doses.

• Usually does not require hospital admission.

• Helps improve the accuracy of long-term monitoring.

• Generally well tolerated by patients.

Possible Side Effects

Side effects are usually mild and temporary, especially with a low dose such as 30 mCi. Some patients may experience:

• Dry mouth

• Altered taste sensation

• Mild nausea

• Fatigue

• Neck discomfort or swelling

• Temporary menstrual changes

These symptoms typically resolve within a short time.

Conclusion

I-131 Radioiodine Therapy – 30 mCi is a surgical alternative that is a safe and effective therapy for selected patients with low-risk differentiated thyroid cancer following thyroidectomy. Treatment locates and eliminates any remaining thyroid tissue, which makes keeping track of thyroid cancer easier in the long run and decreases the risk of recurrence.

The treatment has minimal side effects and excellent results if the patient is well prepared, including elevated TSH and low iodine levels. It is important for patients to educate themselves with their endocrinologist or their nuclear medicine physician to see if this therapy suits them and is appropriate for their situation. At Molecular Diagnostics and Therapy, Dr. Nikunj Jain and the nuclear medicine team provide personalised care and guidance throughout every stage of radioiodine therapy.