Hypothyroidism after radiation exposure: brief narrative review

Area of Science:

• Endocrinology
• Radiation Oncology
• Epidemiology

Background:

• The thyroid gland is highly susceptible to ionizing radiation, with childhood exposure linked to thyroid cancer and nodules.
• Radiation can induce hypothyroidism and autoimmune thyroid disease, though mechanisms are less understood.
• Evidence primarily comes from patient follow-up studies and epidemiological data from radiation-exposed populations.

Purpose of the Study:

• To review the evidence on radiation-induced thyroid dysfunction, including hypothyroidism and autoimmunity.
• To examine dose thresholds for hypothyroidism following different types of radiation exposure.
• To identify knowledge gaps regarding radiation's effects on thyroid function.

Main Methods:

• Literature review of epidemiological studies and patient follow-up data.
• Analysis of studies on survivors of radiation therapy, atomic bombings, and nuclear accidents (e.g., Chernobyl).
• Comparison of dose-response relationships for hypothyroidism after external beam radiotherapy (EBRT) and iodine-131 therapy.

Main Results:

• Childhood radiation exposure clearly increases thyroid cancer risk.
• Hypothyroidism thresholds vary: ~10 Gy for adult EBRT, >50 Gy for iodine-131 therapy, and potentially lower (3-5 Gy) in children exposed during the Chernobyl accident.
• Radiation-induced thyroid autoimmunity is less documented than cancer or hypothyroidism.

Conclusions:

• Radiation exposure poses a significant risk to thyroid function, particularly in children.
• Understanding the varying dose thresholds and underlying mechanisms of radiation-induced hypothyroidism requires further investigation.
• More research is needed on in utero exposure, autoimmunity interactions, and differences between internal and external irradiation.