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 of high risk.

• 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 judgement.

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 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) level elevation. Patients should discuss with their endocrinologist and nuclear medicine physician if 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. 

Test Information

Fasting: 4 hours before therapy

Reporting: Not Applicable

Instructions

• Fast for 4 hours before your scheduled therapy, unless your doctor advises otherwise.

• Drink plenty of water before and after the treatment, unless medically restricted, to help eliminate radioactive iodine from your body.

• Follow a low-iodine diet for 1–2 weeks before therapy, if instructed by your doctor or nuclear medicine specialist.

• Inform your doctor about all medications, thyroid hormone tablets (levothyroxine), anti-thyroid medicines, supplements, iodine-containing medications, recent contrast CT scans, allergies, pregnancy, or breastfeeding, as these may affect treatment.

• If advised, stop thyroid hormone replacement or receive recombinant human TSH (Thyrogen®) injections before therapy, as directed by your doctor.

• Bring your previous thyroid surgery records, biopsy reports, thyroid scan reports, blood test results (TSH, Thyroglobulin, Anti-Thyroglobulin Antibody), and your doctor's prescription on the day of treatment.

• Wear comfortable clothing and arrive at the centre 30–60 minutes before your scheduled appointment.

• Follow all radiation safety instructions provided by the nuclear medicine team after therapy.

निर्देश

• जांच/थेरेपी से 4 घंटे पहले उपवास (फास्टिंग) रखें, जब तक डॉक्टर अन्य निर्देश न दें।

• उपचार से पहले और बाद में, यदि डॉक्टर मना न करें, तो पर्याप्त मात्रा में पानी पिएँ, ताकि रेडियोआयोडीन शरीर से आसानी से बाहर निकल सके।

• यदि डॉक्टर सलाह दें, तो थेरेपी से 1–2 सप्ताह पहले कम आयोडीन वाला आहार (Low-Iodine Diet) अपनाएँ।

• यदि आप थायरॉयड की दवाएँ, अन्य दवाइयाँ, आयोडीन युक्त दवाएँ, सप्लीमेंट ले रहे हैं, हाल ही में कॉन्ट्रास्ट CT स्कैन कराया है, गर्भवती हैं या स्तनपान करा रही हैं, तो इसकी जानकारी डॉक्टर को अवश्य दें।

• डॉक्टर के निर्देशानुसार थायरॉयड हार्मोन दवा (Levothyroxine) कुछ समय के लिए बंद करें या Thyrogen® इंजेक्शन लगवाएँ, यदि सलाह दी गई हो।

• उपचार के दिन अपनी थायरॉयड सर्जरी की रिपोर्ट, बायोप्सी रिपोर्ट, थायरॉयड स्कैन, TSH, Thyroglobulin, Anti-Thyroglobulin Antibody की रिपोर्ट तथा डॉक्टर का प्रिस्क्रिप्शन साथ लेकर आएँ।

• आरामदायक कपड़े पहनकर निर्धारित समय से 30–60 मिनट पहले केंद्र पर पहुँचें।

• उपचार के बाद न्यूक्लियर मेडिसिन टीम द्वारा दिए गए रेडिएशन सुरक्षा निर्देशों का पूरी तरह पालन करें।

Procedure

• Your identity and medical records are verified, and the nuclear medicine specialist reviews your reports before treatment.

• The required I-131 radioactive iodine dose (100 mCi) is administered orally as a capsule or liquid solution.

• After receiving the dose, you may be observed for a short period before discharge or admission, depending on your treatment plan and radiation safety guidelines.

• The radioactive iodine is naturally absorbed by any remaining thyroid tissue or thyroid cancer cells, where it delivers targeted radiation while minimising exposure to most other body tissues.

• You will receive detailed radiation safety instructions to follow after therapy.

• A post-therapy whole-body scan may be performed 3–7 days after treatment, if advised by your doctor, to assess iodine uptake and treatment response.