From the Guidelines
Radiation-induced thyroid cancer is a significant concern for individuals exposed to ionizing radiation, particularly during childhood, and regular monitoring and screening are essential for early detection and treatment. The risk of thyroid cancer is greater in subjects of younger age at exposure, and the incidence of thyroid cancer in children and adolescents was observed to increase as early as 4 years after the Chernobyl accident 1. According to the ESMO clinical practice guidelines for diagnosis, treatment, and follow-up of thyroid cancer, the only established environmental risk factor for thyroid carcinoma is exposure to ionizing radiation 1.
Key points to consider in the management of radiation-induced thyroid cancer include:
- Regular thyroid examinations, including annual physical examinations and thyroid function tests, are recommended for individuals with a history of radiation exposure to the head, neck, or upper chest
- Ultrasound screening should begin 5-10 years after exposure and continue throughout life
- If suspicious nodules are detected, fine needle aspiration biopsy is necessary for diagnosis
- Treatment typically involves total thyroidectomy followed by radioactive iodine therapy to eliminate any remaining thyroid tissue, and lifelong thyroid hormone replacement therapy with levothyroxine (typically starting at 1.6-1.8 mcg/kg/day) 1
The prognosis for radiation-induced thyroid cancer is generally good, with a 10-year survival rate exceeding 90% 1. Prevention focuses on minimizing unnecessary radiation exposure, particularly in children, and using thyroid shields during necessary diagnostic procedures. The latency period between radiation exposure and cancer development ranges from 5-40 years, making long-term monitoring essential for at-risk individuals 1.
From the Research
Radiation-Induced Thyroid Cancer
- The association between radiation exposure and thyroid cancer has been well documented, with the risk increasing after exposure to a mean dose of more than 0.05-0.1 Gy (50-100mGy) 2.
- The risk of thyroid cancer is more important during childhood and decreases with increased age at exposure, being low in adults 2.
- Papillary carcinoma (PTC) is the most frequent form of thyroid carcinoma diagnosed after radiation exposure, with a higher prevalence of the solid subtype in young children with a short latency period and of the classical subtype in cases with a longer latency period after exposure 2.
- Molecular alterations, including intra-chromosomal rearrangements, are frequently found in radiation-induced thyroid cancer, with RET/PTC rearrangements being the most frequent 2.
Latency Period and Dose-Response Relationship
- The minimum latency period before the appearance of thyroid cancers is 5 to 10 years after exposure 2.
- The dose-response relationship for radiation-induced thyroid cancer seems to be linear, with low doses of brief gamma radiation inducing thyroid cancer in juveniles 3.
- The risk of thyroid cancer following low dose and/or protracted exposure to ionizing radiation is a significant concern in radiation protection 3.
Radiation Exposure and Thyroid Cancer Risk
- Studies have shown that children are most at risk from the development of thyroid cancer following exposure to radioactive iodine in fallout from nuclear power plants 4.
- Radioactive iodine (RAI) therapy for hyperthyroidism has been associated with an increased risk of thyroid cancer, with a linear dose-response association between RAI therapy and solid cancer mortality observed in some studies 5.
- However, the overall pooled cancer risk after exposure to RAI therapy vs nonexposure was not significant in a meta-analysis of 12 studies, suggesting that radiation-induced cancer risks following RAI therapy for hyperthyroidism are small 5.