I-131 Treatment: Concerns About Salivary Glands and Dental Health

Many worries, not sure what to do?

Hello, Doctor.
During a lecture, a physician from the nuclear medicine department mentioned that the isotope I-131 can lead to decreased saliva gland secretion, which may increase the risk of dental caries.
Is this primarily associated with high-dose treatment, or does it also occur if no low-dose scans are performed after treatment? I underwent a high-dose I-131 treatment after surgery, but I haven't had any specific low-dose scans in the following two to three years.
Is a low-dose scan typically necessary, or is it sufficient to rely on blood tests for protein levels and ultrasound results that show no abnormalities?
Additionally, if the cumulative dose is too high, could it lead to poor cell differentiation or dedifferentiation in the future? Is the iodine uptake and absorption rate more closely related to age, or is it more dependent on whether the cells are well-differentiated? Does being younger imply better iodine absorption and improved cell differentiation, resulting in a lower risk of recurrence of malignancy?
How long can a single high-dose I-131 treatment remain effective? Can it suppress potential tumor cells effectively? Are the new TKI targeted therapies a result of excessive accumulation of I-131, or do they represent a different treatment approach due to iodine resistance? Thank you for your response, Doctor.

Niming, 20~29 year old female. Ask Date: 2020/12/18

Dr. Zhuang Zhijian reply Nuclear Medicine

Hello! Thank you for your inquiry.
Here are the responses to your questions:
1.
Effects of Iodine-131 on Salivary Glands: Iodine-131 is a radioactive isotope used for diagnosis and treatment, with varying dosages.
(1) For whole-body scans, approximately 2-5 mCi is used; (2) for low-dose treatment of thyroid cancer, about 30 mCi is used; (3) for high-dose treatment of thyroid cancer, doses are greater than 30 mCi, and the dosage for high-dose treatment varies depending on the extent of tumor invasion.
If metastasis is present, treatment doses can range from 100 to 200 mCi depending on the metastatic site.
The effects of Iodine-131 on salivary glands include decreased salivary gland function, acute sialadenitis, chronic sialadenitis, and xerostomia.
Acute sialadenitis may present with localized pain and swelling, which typically resolves after a few days.
The decline in the functional capacity of thyroid follicular cells to produce fluid, combined with scarring from inflammation of the salivary duct, may lead to chronic sialadenitis and xerostomia.
These side effects are more likely to occur after high-dose Iodine-131 treatment.
Past studies from various countries have explored the impact of Iodine-131 on salivary glands.
According to a 2015 study from New Zealand, approximately 16-54% of patients experienced decreased salivary gland function after Iodine-131 treatment.
A 2013 study from the United States indicated that when the treatment dose of Iodine-131 exceeds 100 mCi, xerostomia is related to the treatment dose.
A 2013 study from Korea showed that patients receiving a cumulative dose of Iodine-131 greater than 150 mCi were more likely to experience xerostomia.
A 2016 study from New Zealand found that when the cumulative dose of Iodine-131 was between 100-150 mCi, 34% of patients experienced decreased salivary gland function five months post-treatment.
Another 2013 study from Korea involving 213 post-thyroid cancer surgery patients showed that 16.4% experienced xerostomia five years after receiving 100-150 mCi of radioactive iodine treatment.
These studies indicate that high doses of Iodine-131 can affect salivary gland function, leading to xerostomia due to reduced saliva secretion.
After taking a high dose of Iodine-131, patients can reduce the time Iodine-131 remains in the salivary glands and decrease the incidence of acute sialadenitis and its impact on salivary gland function by sucking on sour candies or lozenges, chewing gum, and drinking plenty of water.
The dosage used for whole-body scans of Iodine-131 is only about 2-5 mCi, which is lower than treatment doses and has limited effects on salivary glands.
2.
Follow-up After Thyroid Cancer Treatment: There are various follow-up methods after thyroid cancer treatment, including physical examinations, blood tests (measuring Thyroid Stimulating Hormone, Thyroglobulin, or anti-thyroglobulin antibodies), neck ultrasound, chest X-ray, whole-body Iodine-131 scans, and positron emission tomography (PET) scans.
Whole-body Iodine-131 scans are commonly used in the following situations: (1) patients who have undergone total thyroidectomy and Iodine-131 treatment; (2) patients at high risk for thyroid cancer recurrence; (3) patients with a history of metastatic tumors that absorbed Iodine-131; (4) when abnormal thyroglobulin levels or elevated anti-thyroglobulin antibodies are detected during follow-up; (5) when abnormalities are found on neck ultrasound.
3.
Differentiated and Undifferentiated Thyroid Cancer: Thyroid cancer can be classified into primary and metastatic types based on pathological diagnosis: (1) Primary thyroid cancer includes the following types: (a) Papillary carcinoma: accounts for about 80% of thyroid cancers and is the most common type, generally growing slowly; (b) Follicular carcinoma: accounts for about 10-15% of thyroid cancers, with tumor cells more likely to metastasize to other organs via the bloodstream; (c) Hurthle cell carcinoma: accounts for about 3-5% of thyroid cancers, with a higher malignancy than papillary and follicular carcinomas, often associated with lymph node and distant organ metastases; (d) Anaplastic carcinoma: accounts for about 1% of thyroid cancers, commonly occurring in individuals over 60 years old, with rapid progression, high invasiveness, and poor prognosis, often diagnosed at a stage where curative surgery is not possible.
The effectiveness of chemotherapy and radiation therapy is also poor; (e) Lymphoma: primarily non-Hodgkin lymphoma.
(2) Metastatic cancer: the most common cancers that metastasize to the thyroid are lung cancer and kidney cancer.
The cause of anaplastic thyroid cancer remains unknown; undifferentiated cancer cells may be related to genetic mutations, and some differentiated thyroid cancer cells may transform into undifferentiated cancer cells.
Current research has not confirmed that patients treated with Iodine-131 have a higher chance of cancer cell transformation.
4.
Mechanism of Iodine Uptake by Cancer Cells: Thyroid cancer cells uptake iodine through the sodium-iodide symporter (NIS) on the cell membrane.
When cancer cells undergo dedifferentiation, the gene for the sodium-iodide symporter may not produce the transporter, resulting in a lack of transporters on the cancer cell membrane, leading to poor iodine uptake or even no uptake.
Therefore, iodine absorption is more closely related to whether the cells are differentiated.
5.
Duration of Iodine-131: The half-life of Iodine-131 is 8 days, so it does not remain in the body for long.
Iodine-131 emits beta radiation, which has the ability to destroy cells and eliminate residual cancer cells after surgery, achieving therapeutic effects.
The range of beta radiation in tissues is approximately 2 mm, which has minimal impact on surrounding normal tissues.
6.
Survival Rates for Thyroid Cancer: The survival rates for thyroid cancer vary based on tumor type and stage.
(1) For papillary thyroid carcinoma, the 5-year survival rate is nearly 100% for stages I and II, approximately 93% for stage III, and about 51% for stage IV, with an overall 10-year survival rate of about 93%.
Papillary and follicular thyroid cancers have very favorable prognoses.
(2) For follicular thyroid carcinoma, the 5-year survival rate is nearly 100% for stages I and II, approximately 71% for stage III, and about 50% for stage IV, with an overall 10-year survival rate of about 85%.
(3) For medullary thyroid carcinoma, the 5-year survival rate is about 100% for stage I, approximately 98% for stage II, about 81% for stage III, and about 28% for stage IV, with an overall 10-year survival rate of about 75%.
(4) For anaplastic thyroid carcinoma, patients are often diagnosed at stage IV, with a 5-year survival rate of only about 7%.
7.
Risk of Thyroid Cancer Recurrence: The risk of thyroid cancer recurrence is influenced by tumor characteristics.
The risk is higher in cases of invasion into surrounding thyroid tissues, distant metastasis, local lymph node metastasis greater than 3 cm, and when cancer cells spread via the bloodstream.
8.
Tyrosine Kinase Inhibitors: Treatment for thyroid cancer includes surgery, radioactive iodine therapy, medication, radiation therapy, chemotherapy, and targeted therapy.
For differentiated thyroid cancer, most patients have good outcomes through surgical removal of the lesions, radioactive iodine therapy, and long-term thyroid hormone replacement.
However, for patients with poor treatment responses, including more aggressive cell types, more invasive tumor characteristics, cancer cells that do not absorb radioactive iodine, or those who have reached the cumulative dose limit of radioactive iodine treatment without clearing cancer cells, tyrosine kinase inhibitors (TKIs) are one of the treatment options.
TKIs can inhibit signaling pathways related to cell proliferation within cancer cells and can also inhibit angiogenesis, preventing new blood vessels from continuously supplying nutrients to the tumor, thereby controlling cancer cells and extending patient survival.

Reply Date: 2020/12/18

More Info

I-131 treatment, commonly used for conditions such as hyperthyroidism and thyroid cancer, involves the administration of radioactive iodine to target thyroid tissue. While this treatment can be effective, it does raise several concerns, particularly regarding salivary gland function and dental health.

One of the well-documented side effects of I-131 treatment is its impact on the salivary glands. The radioactive iodine can lead to a decrease in saliva production, which may increase the risk of dental issues, including cavities and oral infections. This risk is particularly pronounced in patients who receive high doses of I-131, as higher radiation exposure can cause more significant damage to the salivary glands. However, even lower doses can have an effect, especially if the treatment is repeated over time.

Regarding your question about the necessity of follow-up scans after I-131 treatment, it is generally recommended to have periodic evaluations to monitor thyroid function and check for any recurrence of disease. While blood tests and ultrasounds can provide valuable information, they may not always be sufficient to rule out all potential issues. Small dose scans can help assess the thyroid's uptake of iodine and ensure that there are no residual or recurrent thyroid cells that could lead to complications.
As for the concerns about cumulative radiation exposure and its effects on cellular differentiation, it is important to note that while radiation can influence cellular behavior, the relationship is complex. Factors such as age, overall health, and the specific characteristics of the thyroid tissue can all play a role in how the body responds to radiation. Younger patients may have a better capacity for cellular repair and differentiation, but this does not guarantee that they will be free from complications or recurrence of disease.

The effectiveness of a single high dose of I-131 can vary, but it is generally expected to provide long-term control of thyroid conditions. The duration of effectiveness can depend on various factors, including the initial condition being treated, the dose administered, and individual patient factors. In some cases, additional treatments may be necessary if there is evidence of persistent or recurrent disease.

Finally, the introduction of newer targeted therapies, such as tyrosine kinase inhibitors (TKIs), represents a shift in treatment approaches for thyroid cancer and other malignancies. These therapies may be used in conjunction with or as an alternative to I-131, depending on the specific characteristics of the cancer and the patient's overall treatment plan. The choice of therapy is often influenced by the tumor's response to previous treatments, including I-131, and the presence of specific genetic mutations that may affect treatment efficacy.

In summary, while I-131 treatment can be effective, it is essential to monitor its effects on salivary gland function and dental health. Regular follow-up appointments, including scans and blood tests, are crucial for ensuring ongoing health and addressing any potential complications. If you have concerns about your treatment plan or the risks associated with I-131, it is advisable to discuss them with your healthcare provider, who can provide personalized guidance based on your medical history and current health status.

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