I-131 Radioiodine Therapy – 100 mCi

I-131 Radioiodine Therapy – 100 mCi is a form of targeted nuclear medicine therapy employed in patients with differentiated thyroid cancer, including papillary thyroid cancer and follicular thyroid cancer (after thyroidectomy). It is also used in selected patients with persistent or recurrent thyroid cancer, as indicated clinically.

A few pieces of thyroid (or tiny pieces of cancer) may be left in the body after surgery. Radioiodine therapy employs naturally taken-up radioactive iodine (I-131) to kill the remaining thyroid cells and cause minimal damage to most tissues around the thyroid gland.

At Molecular Diagnostics and Therapy, Dr. Nikunj Jain, Co-Founder and HOD – Nuclear Medicine, provides expert evaluation and personalised radioiodine treatment planning for patients requiring I-131 therapy after thyroid cancer surgery. 100 mCi is a therapeutic dose and is administered to patients with intermediate- and high-risk thyroid cancer who have had the thyroid gland removed and to patients who have undergone thyroid remnant ablation.

Understanding I-131 and Its Therapeutic Role

Radioactive iodine (I-131) selectively kills thyroid tissue and thyroid cancer cells, emitting beta radiation. I-131 therapy is used after a thyroidectomy to:

• Remove any remaining thyroid.

• Remove thyroid cancer cells that are too small.

• Decrease the chances of it recurring.

• Create a more accurate system of monitoring thyroglobulin in serum.

• Improve ability to interpret future diagnostic scanning results.
  
  

There is a satisfactory safety profile with a dosage of 100 mCi when given under the supervision of a specialist.

Why is the 100 mCi Dose Used?

A 100 mCi dose may be recommended in several clinical situations, including:

• Post-thyroid surgery (total or near-total).

• Intermediate-risk differentiated thyroid cancer.

• Selected patients with high-risk thyroid cancer.

• Patients who have thyroid tissue left after surgery.

• Thyroglobulin elevated – residual disease.

• When this dose is deemed suitable for the treating specialist for patients without extensive distant metastatic disease.
  
  

The final dose is also dependent on the patient's condition and treatment objective and is based on the nuclear medicine physician's judgment.

Preparation Before I-131 Radioiodine Therapy – 100 mCi

Again, proper preparation can ensure the greatest "hit" of radioactive iodine on remaining thyroid tissue.

1. Elevation of TSH (Thyroid-Stimulating Hormone)

With treatment, TSH levels should be elevated (>30 mIU/L) before starting treatment. Increased TSH increases how well the remaining thyroid tissue takes up radioiodine. Two methods are commonly used:

Thyroid Hormone Withdrawal

Patients stop taking thyroid hormone medication (such as levothyroxine) for 3–4 weeks before therapy. This causes temporary hypothyroidism, leading to increased TSH levels. Possible symptoms include:

• Fatigue

• Weight gain

• Cold intolerance

• Constipation

• Low mood

• Slower heart rate

These symptoms usually improve once thyroid hormone therapy is restarted.

Recombinant Human TSH (Thyrogen®)

Another option is recombinant human TSH injections administered over two consecutive days before treatment. Benefits include:

• Patients can continue thyroid hormone medication.

• Avoids hypothyroid symptoms.

• Suitable for elderly patients and those with other medical conditions.

Your doctor will recommend the most appropriate preparation method.

2. Low-Iodine Diet

Patients are usually advised to follow a low-iodine diet for 1–2 weeks before treatment. This helps improve radioactive iodine uptake.

Foods to Avoid

• Iodized salt and sea salt

• Dairy products

• Seafood and seaweed

• Egg yolks

• Soy products

• Foods containing red food dye

• Multivitamins containing iodine

Foods Allowed

• Fresh fruits and vegetables

• Egg whites

• Plain rice and pasta

• Non-iodized salt

• Fresh meat and poultry without additives

How is I-131 Radioiodine Therapy (100 mCi) Administered?

The therapy is usually administered orally as a capsule or, less commonly, as a liquid. Important points include:

• Typically, patients will be instructed to abstain from food/drink for approximately 4 hours before and after treatment.

• Short hospitalisation and outpatient treatment can be recommended based on the radiation safety rules of the institution.

• Patients are monitored following administration.

The radioactive iodine enters the bloodstream and is selectively absorbed by the remaining thyroid tissue and thyroid cancer cells.

Radiation Safety Guidelines

Following treatment, patients should follow radiation safety precautions for the period advised by their treating physician. These may include:

• Avoid close contact with children and pregnant women.

• Sleep separately for several days.

• Use separate towels and utensils where possible.

• Flush the toilet twice after use.

• Wash hands thoroughly after using the toilet.

• Drink plenty of fluids to help eliminate radioactive iodine.

Detailed written instructions will be provided by the nuclear medicine department.

What Happens After the Therapy?

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

• Confirm uptake in residual thyroid tissue.

• Detect unexpected areas of radioactive iodine uptake.

• Assess treatment effectiveness.

Long-term follow-up may include:

• Serum thyroglobulin blood tests.

• TSH and thyroid hormone monitoring.

• Neck ultrasound.

• Additional imaging when clinically indicated.

Benefits of I-131 Radioiodine Therapy – 100 mCi

• Effective treatment for differentiated thyroid cancer.

• Helps destroy remaining thyroid tissue and microscopic cancer cells.

• Reduces the risk of recurrence.

• Improves long-term disease monitoring.

• Targeted treatment with minimal effect on most normal tissues.

• Generally well tolerated.

Possible Side Effects

Most side effects are temporary and mild. Some patients may experience:

• Nausea

• Fatigue

• Neck discomfort or swelling

• Dry mouth

• Altered taste sensation

• Salivary gland swelling

• Temporary menstrual irregularities

There are very few complications that can arise, and the treating physician will discuss these with you before therapy.

Conclusion

Treatment with one hundred (100mCi) units of Iodine 131 is a safe and effective option for selected thyroid cancer patients after thyroidectomy. Therapy selectively destroys the remaining thyroid tissue and the microscopic cancer cells, thus making the chance of recurrence smaller and making the long-term follow-up more reliable. This therapy can be used effectively if administered properly, with a general low-iodine diet, and using thyroid-stimulating hormone (TSH) levels. 

Patients should discuss with their endocrinologist and nuclear medicine physician whether a dose of 100 mCi is the right choice for them. At Molecular Diagnostics and Therapy, Dr. Nikunj Jain and the nuclear medicine team provide comprehensive treatment planning, personalised care, and long-term follow-up throughout the radioiodine therapy journey.