I-131 Radioiodine therapy - 200 mCi

I-131 Radioiodine Therapy is a well-established and effective treatment modality used for eliminating residual thyroid tissue or thyroid cancer cells after surgical removal of the thyroid gland (thyroidectomy). The therapy utilizes radioactive iodine (I-131), which is selectively absorbed by thyroid cells due to their natural affinity for iodine. Administered in controlled dosages, such as 200 mCi, this targeted therapy emits beta radiation, which destroys remaining thyroid cells, thereby reducing the risk of recurrence or metastasis. This form of therapy is also referred to as radioiodine ablation.

How I-131 Radioiodine Therapy Works

The thyroid gland uses iodine to produce hormones that regulate metabolism. After a total or near-total thyroidectomy, small amounts of thyroid tissue often remain in the thyroid bed or may have spread elsewhere (metastases). These residual tissues, like the original thyroid gland, continue to absorb iodine.  By administering radioactive iodine (I-131), these remaining cells absorb the radioactive substance. The emitted beta particles effectively destroy the residual cells, helping prevent recurrence and aiding long-term disease control.

Indications for I-131 Radioiodine Therapy – 200 mCi

This therapy is primarily indicated in the following conditions:

• Ablation of remnant thyroid tissue after thyroidectomy
• Treatment of differentiated thyroid carcinoma, including papillary and follicular types
• Metastatic thyroid cancer to lungs, bones, or lymph nodes
• Reducing serum thyroglobulin levels in follow-up monitoring
• Eradicating microscopic disease not visible on scans
• High-risk recurrence patients, especially those with aggressive tumour features

Preparation Before I-131 Therapy

For the radioactive iodine therapy to be most effective, it is crucial that Thyroid Stimulating Hormone (TSH) levels are adequately elevated. This stimulates iodine uptake by the remaining thyroid cells.

There are two main methods to achieve elevated TSH levels:

1. Thyroid Hormone Withdrawal Method

• Stop Thyronorm or similar thyroid hormone medications for 3 to 6 weeks before therapy
• This leads to hypothyroidism, which naturally elevates TSH levels
• Side effects of hypothyroidism may include:

• Fatigue
• Cold intolerance
• Constipation
• Mood changes
• Weight gain
  • This is a cost-effective method, widely used especially when Thyrogen® is not available

2. Recombinant TSH (Thyrogen®) Injections

• Two intramuscular injections of synthetic TSH (Thyrogen®) are administered 24 hours apart
• Radioiodine is given 24 hours after the second injection
• The patient continues Thyronorm, avoiding the symptoms of hypothyroidism
• This method improves quality of life during therapy preparation but may be costlier

Both approaches have advantages and should be discussed with your treating physician to determine the best method for your case.

Procedure for I-131 Radioiodine Therapy – 200 mCi

1. Pre-therapy evaluation

• TSH level assessment
• Low-iodine diet for 1–2 weeks
• Blood tests including serum thyroglobulin and renal function
• Pregnancy test (mandatory for women of reproductive age)

2. Hospital admission

• Typically a single-day or short-stay admission in an isolation ward
• Patients are kept in a shielded room to prevent radiation exposure to others

3. Radioiodine Administration

• Administered orally, usually in capsule or liquid form
• Swallowed with water under supervision

4. Post-administration instructions

• Patients remain in isolation for 1–3 days
• Hydration is encouraged to flush out radioactive material
• Toileting and personal hygiene guidelines provided to prevent contamination
• Radiation exposure monitored before discharge

Post-Therapy Recommendations

• Maintain distance from others, especially children and pregnant women for a few days
• Resume thyroid hormone medication as advised
• Follow a low-iodine diet if instructed
• Avoid pregnancy for at least 6 months post-therapy
• Regular follow-up with:

• Thyroglobulin tests
• Neck ultrasound
• Whole-body I-131 scans

Benefits of I-131 Radioiodine Therapy

• Targeted ablation of residual thyroid tissue
• Improves long-term survival in differentiated thyroid carcinoma
• Reduces recurrence risk by destroying microscopic or hidden cancer cells
• Safe and non-invasive oral treatment
• Short hospital stay and manageable side effects
• Can be repeated in case of recurrence or metastases

Possible Side Effects

I-131 Radioiodine therapy is generally safe, but side effects may include:

• Mild neck discomfort or swelling
• Temporary dry mouth or altered taste
• Nausea or abdominal pain
• Sore throat or salivary gland swelling
• Transient changes in menstrual cycle
• Very rare risk of secondary malignancies or infertility with repeated high-dose exposure

Radiation precautions ensure the safety of both patients and their families during and after therapy.

Conclusion

I-131 Radioiodine Therapy – 200 mCi is a highly effective post-surgical treatment in differentiated thyroid cancer. By utilizing the thyroid’s natural ability to absorb iodine, this therapy safely eliminates residual tissues and possible metastases. Whether approached through thyroid hormone withdrawal or recombinant TSH injection, it plays a vital role in reducing recurrence and improving long-term outcomes. Patients benefit from a targeted, minimally invasive, and scientifically proven method of cancer care. With appropriate preparation, monitoring, and post-care follow-up, radioiodine therapy offers a powerful tool in the successful treatment and management of thyroid cancer. If you have undergone thyroidectomy or been diagnosed with differentiated thyroid carcinoma, consult your nuclear medicine specialist to evaluate if I-131 therapy is right for you.