the Long-Term Effects of I-131 Treatment in Thyroid Cancer Patients

May I ask the doctor?

Hello, Doctor.
Due to PTC, I underwent a total thyroidectomy and received a 120 mCi dose of I-131.
For the past two to three years, my follow-ups have included ultrasound, serum thyroglobulin, TSH, and FT4 tests.
I would like to ask if radioactive iodine treatment increases the risk of infertility, pulmonary fibrosis, or leukemia in the future? Is there a safe cumulative dose of iodine over a lifetime? How often are low-dose iodine scans typically performed? Is it true that if there are no abnormalities in blood tests or ultrasound, low-dose scans may not be necessary? Could iodine exposure potentially lead to ovarian failure or an increased risk of genetic mutations? It seems that some hospitals have nuclear medicine departments for follow-ups, while others have surgical or internal medicine departments.
How often should I typically return for outpatient visits? Why can some people return every year or every six months, while others need to come back in just a few months? Is it really not feasible to get medication from a small clinic? Thank you, Doctor, for patiently reading my questions.

Niming, 20~29 year old female. Ask Date: 2020/12/15

Dr. Chen Sirong reply Oncology

Anonymous / 25 years old / Female
1.
I would like to ask if radioactive iodine treatment increases the future risk of infertility, pulmonary fibrosis, or leukemia?
ANS: Potential side effects of radioactive iodine treatment include thyroiditis, which may occur if there is a significant amount of residual thyroid tissue after surgery, potentially causing neck swelling and pain.
However, these symptoms can often be alleviated with anti-inflammatory medications.

Salivary gland inflammation may occur as the salivary glands also absorb some radioactive iodine, leading to symptoms such as swelling, pain, a bitter taste, and dry mouth.
Acidic lozenges or beverages can help expedite salivary gland clearance and reduce the risk of inflammation.

Gastrointestinal discomfort may present as temporary loss of appetite, nausea, and vomiting, which can be managed with gastrointestinal medications.

Bone marrow suppression may affect blood cell production, resulting in a temporary decrease in blood cell counts, typically resolving within 2 to 3 months.
This situation is more common in patients with multiple bone metastases who have received multiple high-dose treatments, but the incidence is very low.

Regarding reproductive health, male patients may experience a temporary decrease in sperm count, which will recover on its own; female patients' fertility is not affected.
Given that you have been monitored for 2-3 years, it is likely that there are no treatment-related side effects.
2.
Is there a safe cumulative dose of iodine over a lifetime?
ANS: 800 mCi.
3.
How often should low-dose iodine scans be performed?
ANS: Every six months to once a year.
4.
Will low-dose scans still be conducted if there are no abnormalities in blood tests or ultrasounds?
ANS: I would still arrange for scans, as sensitivity can vary.
5.
Is there a risk of ovarian failure or increased likelihood of genetic mutations due to iodine exposure?
ANS: The treatment doses are relatively high, and it is recommended to avoid pregnancy for 3-6 months post-treatment.
However, since the doses are low, contraception may not be necessary.
There is no evidence to support concerns about ovarian failure or genetic mutations.
6.
How often should I return for follow-up appointments?
ANS: Typically, visits are monthly for the first three months, then every two months, three months, or even six months thereafter.
Since you have been monitored for 2-3 years, you can return every 3-6 months.
7.
Is it really not advisable to obtain medication from a small clinic?
ANS: It is recommended to have long-term follow-up at a larger hospital.
If you need to obtain medication long-term, a chronic prescription can be arranged for every three months.
Wishing you peace and health,
Taoyuan Hospital
Dr.
Chen Sih-Rong

Reply Date: 2020/12/15

More Info

The long-term effects of I-131 (radioactive iodine) treatment in thyroid cancer patients, particularly those with papillary thyroid carcinoma (PTC), are a significant concern for both patients and healthcare providers. After undergoing a total thyroidectomy followed by a high-dose I-131 treatment, it is essential to monitor for potential long-term complications and understand the implications of the treatment on overall health.

1. Increased Risk of Infertility and Other Conditions: There is ongoing research regarding the long-term effects of I-131 treatment on fertility, lung fibrosis, and leukemia. While some studies suggest that high doses of radioactive iodine may have an impact on fertility, particularly in women, the evidence is not definitive. The risk of infertility may be influenced by the total cumulative dose of I-131 received, as well as individual patient factors such as age and pre-existing health conditions.
Regarding lung fibrosis, there is limited evidence linking I-131 treatment directly to this condition. However, patients should be aware of any respiratory symptoms and discuss them with their healthcare provider. The risk of leukemia, particularly in patients who have received high doses of radiation, is a concern, but the incidence remains relatively low in thyroid cancer patients treated with I-131.

2. Cumulative Dose and Safety Limits: The total cumulative dose of iodine-131 that is considered safe varies among individuals and is influenced by factors such as age, sex, and overall health. There is no universally accepted "safe" limit for total iodine exposure, but healthcare providers typically aim to minimize radiation exposure while effectively treating the cancer. Regular follow-up with blood tests (such as thyroglobulin and TSH levels) and imaging studies (like ultrasound) is crucial for monitoring thyroid cancer recurrence and managing any potential side effects of treatment.

3. Frequency of Scans and Monitoring: For patients who have undergone I-131 treatment, the frequency of follow-up scans and blood tests can vary. Generally, if there are no abnormalities detected in blood tests or ultrasound examinations, the frequency of imaging studies may be reduced. Some patients may only need to undergo low-dose iodine scans annually or biannually, while others may require more frequent monitoring based on their individual risk factors and clinical history.
4. Concerns About Ovarian Function and Genetic Mutations: There is limited evidence to suggest that I-131 treatment significantly increases the risk of ovarian failure or genetic mutations. However, any concerns regarding reproductive health should be discussed with a healthcare provider, particularly for women of childbearing age. Genetic counseling may also be beneficial for patients worried about hereditary risks.

5. Follow-Up Care: The follow-up care for thyroid cancer patients can vary significantly depending on the healthcare system and the individual patient's needs. Some patients may be seen every few months, while others may have appointments spaced out over a year or more. The decision on follow-up frequency often depends on the patient's risk of recurrence, the results of previous tests, and the healthcare provider's recommendations. It is essential to maintain open communication with your healthcare team and express any concerns about the frequency of visits or the management of your care.

In conclusion, while I-131 treatment is an effective therapy for thyroid cancer, it is crucial to remain vigilant about potential long-term effects. Regular follow-up with healthcare providers, adherence to monitoring protocols, and open discussions about any concerns can help manage risks and ensure the best possible outcomes for thyroid cancer survivors.

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