What are the complications of thyroid radiation exposure?

From the Guidelines

Complications of thyroid radiation are a significant concern, and patients exposed to radiation should be closely monitored for both acute and long-term effects, including hypothyroidism, secondary malignancies, and radiation fibrosis, as highlighted in studies such as 1.

Acute Complications

Acute complications of thyroid radiation typically occur during or shortly after treatment and include:

• Radiation thyroiditis, causing pain and swelling
• Skin irritation
• Fatigue
• Difficulty swallowing
• Hoarseness
• Dry mouth These complications are often temporary but can significantly impact the patient's quality of life.

Long-term Complications

Long-term complications are more concerning and include:

• Hypothyroidism, occurring in 20-30% of patients within 5 years, which requires lifelong thyroid hormone replacement therapy, typically levothyroxine at doses of 1.6-1.8 mcg/kg/day, as noted in 1
• Secondary malignancies, particularly in younger patients, with risks persisting for decades after exposure
• Radiation fibrosis, which may develop in surrounding tissues, potentially affecting the esophagus, trachea, and blood vessels, leading to swallowing difficulties or voice changes
• Salivary gland dysfunction, causing dry mouth and increased dental problems

Monitoring and Prevention

Patients who receive thyroid radiation should undergo regular thyroid function testing (TSH, free T4) every 6-12 months to monitor for hypothyroidism and should have annual physical examinations to check for signs of secondary cancers or other complications, as recommended in studies such as 1. Thyroid blocking with potassium iodide offers some protection, particularly in cases of radioiodine exposure, by reducing radioiodine uptake by 50% when administered within 4 hours of the exposure, as stated in 1. However, potassium iodide is not a generic antiradiation drug and should only be used in cases where radioiodines are part of the exposure. In pregnant women, thyroid protection is critical, and stable iodine or potassium iodide may be used depending on the trimester and type of exposure, as discussed in 1.

From the FDA Drug Label

In a nuclear radiation emergency, radioactive iodine may be released in the air. This material may be breathed or swallowed. It may enter the thyroid gland and damage it. The damage would probably not show itself for years. Children are most likely to have thyroid damage. The main complication of thyroid radiation is thyroid damage, which may not be apparent for years. This damage is more likely to occur in children. The damage is caused by the uptake of radioactive iodine by the thyroid gland. 2

• Key points:
  • Thyroid damage from radiation may be delayed
  • Children are at higher risk
  • Radioactive iodine is the cause of the damage

From the Research

Complications of Thyroid Radiation

• Radiation exposure to the thyroid gland can lead to various complications, including hypothyroidism, thyroid nodules, and thyroid cancer 3, 4, 5, 6, 7
• High-dose radiation exposure, such as that from external beam radiotherapy or radioiodine therapy, can destroy the thyroid gland and induce autoantibodies against thyroid tissue 3
• The risk of hypothyroidism increases with higher doses of radiation, with threshold doses of around 10 Gy after external beam radiotherapy and 50 Gy after radioiodine therapy 3
• Children and adolescents are more sensitive to the effects of radiation on the thyroid gland than adults 3, 5
• Radiation-induced hypothyroidism can be treated with thyroid hormone replacement therapy, which can ensure normal life expectancy if dosing and monitoring are individualized and regular 3

Radiation-Induced Thyroid Changes

• Incidental or therapeutic thyroid irradiation can cause hypothyroidism and nodular disease 6
• Early diagnosis and treatment of radiation-related thyroid changes are important, particularly in children who have been cured of cancers by treatments that include radiation to the thyroid bed 6
• Prospective evaluation of patients given thyroid irradiation can help identify and treat any radiation-related thyroid changes promptly 6

Risk of Hypothyroidism due to Irradiation

• The risk of hypothyroidism due to irradiation of the thyroid and pituitary glands has been reported in patients undergoing radiotherapy for nasopharyngeal cancer 7
• Patients with high thyroid and pituitary gland doses are at higher risk of abnormal thyroid physiology, with the dose to the thyroid being more influential than the pituitary dose 7
• Attention should be given to the thyroid gland in radiotherapy planning to minimize the risk of hypothyroidism 7