I-131 Radioiodine Therapy – 50 mCi

I-131 Radioiodine Therapy–50 mCi

Targeted nuclear medicine treatment, I-131 Radioiodine Therapy–50 mCi, is most often used in patients who have had a thyroidectomy for differentiated thyroid cancer (papillary thyroid cancer or follicular thyroid cancer). Following thyroid surgery, there may be some thyroid tissue left in the body or microscopic cancer cells. Radioiodine therapy uses radioactive iodine (I-131), which the thyroid naturally absorbs and kills off these remaining cells.

At Molecular Diagnostics and Therapy, Dr. Nikunj Jain, Co-Founder and HOD – Nuclear Medicine, provides expert evaluation and personalised radioiodine treatment planning for patients undergoing I-131 Radioiodine Therapy after thyroid cancer surgery. 

This therapy takes advantage of the thyroid cells' natural tendency to take up iodine and delivers iodine with very precise targeting to the remaining thyroid cells, thereby lowering the risk of recurrence and facilitating more effective long-term monitoring with serum thyroglobulin markers and imaging. A medium dose of 50 mCi is typically the recommended dose for low-to intermediate-risk patients following thyroid surgery and is used for thyroid remnant ablation.

Understanding I-131 and Its Therapeutic Role

Radioactive iodine (I-131) is a therapeutic isotope that emits beta radiation (beta-131), which is more likely to damage parts of the thyroid gland, but does not affect most of the surrounding tissues. After surgery for the thyroid, the following therapies are given with I-131:

• Destroy any remaining normal thyroid tissue.

• Eliminate microscopic cancer cells not removed during surgery.

• Improve the accuracy of future follow-up tests, such as thyroglobulin levels.

• Enable better interpretation of diagnostic scans.

• Reduce the risk of recurrence in differentiated thyroid cancer.

The use of 50 mCi of I-131 safely ablates small amounts of thyroid tissue without harming the normal thyroid gland.

Why is the 50 mCi Dose Used?

A 50 mCi dose may be recommended in several clinical situations, including:

• Thyroid remnant ablation after total or near-total thyroidectomy.

• Low-risk or selected intermediate-risk thyroid cancer patients.

• Patients with minimal residual thyroid tissue.

• Cases where improved follow-up monitoring using thyroglobulin testing is required.

• Patients without evidence of distant metastasis.

Situations when a better follow-up of patients by performing thyroglobulin testing is warranted.

Preparation Before I-131 Radioiodine Therapy – 50 mCi

This amount will achieve effective tissue destruction with reasonable radiation dose exposure, versus higher therapeutic doses.

1. Elevation of TSH (Thyroid-Stimulating Hormone)

Appropriate preparation is essential for success. The two big achievements are when the TSH is elevated and when a low iodine diet is performed.

Thyroid Hormone Withdrawal

Reversible therapy is discontinued thyroid hormone use (such as levothyroxine) for 3–4 weeks before therapy. This makes TSH rise, because it causes temporary hypothyroidism. Some symptoms during this time may involve:

• Fatigue

• Weight gain

• Cold intolerance

• Constipation

• Low mood

• Slower heart rate

These symptoms usually resolve once thyroid hormone therapy is restarted.

Recombinant Human TSH (Thyrogen®)

You can also have the recombinant human TSH injections two days apart before therapy. Advantages include:

• Patients can continue taking thyroid hormone medication.

• Avoids symptoms of hypothyroidism.

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

Your doctor will determine the most appropriate preparation method.

2. Low-Iodine Diet

A low-iodine diet is typically recommended before therapy for 1-2 weeks. This lowers the uptake of radioactive iodine by the remaining thyroid cells and the iodine levels in the body.

Foods to Avoid

• Iodized salt and sea salt

• Dairy products (milk, cheese, yogurt, butter)

• Egg yolks

• Seafood and seaweed

• Soy products

• Foods containing red food dye

• Multivitamins containing iodine

Allowed Foods

• Fresh fruits and vegetables

• Plain rice and pasta

• Egg whites

• Non-iodized salt

• Fresh meat and poultry without additives

How is I-131 Radioiodine Therapy (50 mCi) Administered?

This therapy is typically given by mouth in the form of a capsule but can be given as a liquid. Important points include:

• Patients are usually asked to fast for about 4 hours before and after the dose.

• Most patients receiving 50 mCi can be treated on an outpatient basis, depending on institutional regulations.

• A brief observation period may follow administration.

After injection, the radioactive iodine enters the bloodstream and is taken up by the remaining thyroid tissue.

Radiation Safety Guidelines

Patients may receive some instructions that they need to take precautions for the first 3–5 days after treatment, although the radiation levels can be relatively low.

• Avoid close contact with children and pregnant women.

• Sleep separately from others for a few days.

• Use separate towels and utensils if possible.

• Flush the toilet twice after use.

• Wash your hands frequently and maintain good hygiene.

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

Your team of nuclear medicine practitioners will give you specific safety guidelines suitable for your case.

What Happens After the Therapy?

Whole-body scans may also be done after therapy with iodine to check that the iodine is being taken up, which usually occurs 3-7 days after treatment. This scan helps to:

• Confirm uptake in residual thyroid tissue.

• Identify any unexpected areas of iodine uptake.

• Assess the success of the ablation.

Long-term follow-up typically includes:

• Serum thyroglobulin testing (an important tumour marker).

• TSH and thyroid hormone level monitoring.

• Neck ultrasound or other imaging studies, if needed.

Benefits of I-131 Radioiodine Therapy – 50 mCi

• Minimally invasive treatment.

• Often performed as an outpatient procedure.

• Effective for thyroid remnant ablation after thyroid surgery.

• Helps improve the accuracy of long-term monitoring.

• Lower risk of side effects compared with higher therapeutic doses.

• Generally well tolerated by patients.

Possible Side Effects

Side effects with a 50 mCi dose are usually mild and temporary. Some patients may experience:

• Nausea

• Fatigue

• Mild neck discomfort or swelling

• Dry mouth or altered taste

• Temporary menstrual irregularities

These symptoms typically resolve within a short period.

Conclusion

When differentiated thyroid cancer is diagnosed, I-131 Radioiodine Therapy – 50 mCi may be an important treatment option for those patients after undergoing thyroidectomy. The treatment eliminates any thyroid tissue left behind and microscopic thyroid cancer cells, thereby minimizing the chance of thyroid cancer recurrence and increasing the effectiveness of thyroid monitoring.

This therapy is then a safe, effective, and targeted approach to the management of post-surgery thyroid cancer with proper management steps, such as when TSH is elevated, and following a low iodine diet. Patients should always ask their endocrinologist or nuclear medicine specialist if they are suitable for this treatment for their individual case. 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 at least 4 hours before the therapy, unless your nuclear medicine specialist advises otherwise.

• Follow the low-iodine diet recommended by your doctor, usually for 1–2 weeks before treatment, to improve the uptake of radioactive iodine by the remaining thyroid tissue.

• Your TSH level may need to be adequately elevated before therapy. Follow your doctor's instructions regarding thyroid hormone withdrawal or recombinant human TSH (rhTSH) injections.

• Inform your doctor about all medications, supplements, vitamins, herbal products, and any recent iodine-containing medicines or contrast studies, as these may affect treatment.

• Do not stop or restart thyroid hormone medication unless specifically instructed by your doctor.

• Inform your doctor if you are pregnant, think you may be pregnant, or are breastfeeding. I-131 Radioiodine Therapy must not be administered during pregnancy, and breastfeeding should be discontinued as advised before treatment.

• Carry your previous thyroid function tests, thyroglobulin reports, neck ultrasound, biopsy reports, surgical records, previous thyroid scans, and your doctor's prescription, if available.

• Arrive at the centre 10–15 minutes before your scheduled appointment for registration and preparation.

निर्देश

• उपचार से पहले कम से कम 4 घंटे का फास्टिंग रखें, जब तक आपके न्यूक्लियर मेडिसिन विशेषज्ञ अन्य निर्देश न दें।

• उपचार से पहले आमतौर पर 1–2 सप्ताह तक लो-आयोडीन डाइट का पालन करें, जैसा आपके डॉक्टर द्वारा बताया गया हो, ताकि रेडियोआयोडीन का अवशोषण बेहतर हो सके।

• उपचार से पहले आपका TSH स्तर पर्याप्त रूप से बढ़ा हुआ होना आवश्यक हो सकता है। थायरॉइड हार्मोन की दवा बंद करने या recombinant human TSH (rhTSH) इंजेक्शन के संबंध में डॉक्टर के निर्देशों का पालन करें।

• यदि आप कोई दवाइयाँ, विटामिन, सप्लीमेंट, हर्बल उत्पाद या हाल ही में आयोडीन युक्त दवा या कॉन्ट्रास्ट जांच करवा चुके हैं, तो इसकी जानकारी डॉक्टर को अवश्य दें।

• डॉक्टर की सलाह के बिना थायरॉइड हार्मोन की दवा बंद या दोबारा शुरू न करें।

• यदि आप गर्भवती हैं, गर्भवती होने की संभावना है या स्तनपान करा रही हैं, तो डॉक्टर को अवश्य बताएं। गर्भावस्था में यह उपचार नहीं किया जाता तथा उपचार से पहले स्तनपान डॉक्टर की सलाह अनुसार बंद करना आवश्यक है।

• अपनी पुरानी थायरॉइड फंक्शन टेस्ट रिपोर्ट, थायरोग्लोबुलिन रिपोर्ट, नेक अल्ट्रासाउंड, बायोप्सी रिपोर्ट, सर्जरी रिकॉर्ड, पुरानी थायरॉइड स्कैन रिपोर्ट और डॉक्टर का प्रिस्क्रिप्शन साथ लेकर आएं।

• पंजीकरण और तैयारी के लिए निर्धारित समय से 10–15 मिनट पहले केंद्र पर पहुंचें।

Procedure

• Before treatment, the nuclear medicine specialist reviews your medical history, laboratory results, imaging findings, and confirms that you have completed the required preparation.

• The prescribed 50 mCi dose of I-131 Radioiodine is administered orally as a capsule or liquid.

• The radioactive iodine is absorbed into the bloodstream and selectively taken up by any remaining thyroid tissue or iodine-avid thyroid cancer cells.

• The therapy is painless and usually completed within a few minutes. A short observation period may be required after administration.

• You will receive personalised radiation safety instructions regarding contact with family members, personal hygiene, sleeping arrangements, travel, and other precautions after treatment.

• Drink plenty of fluids, unless medically restricted, to help eliminate the remaining radioactive iodine from your body.

• A post-therapy whole-body scan may be performed a few days after treatment, depending on your doctor's recommendation.

• Follow-up may include thyroglobulin blood tests, thyroid function tests, neck ultrasound, and additional imaging, as advised by your doctor.