A CT scan uses ionizing radiation to create detailed images of the body, including the neck area where the thyroid gland is located. The radiation involved in a CT scan can expose the thyroid gland to scattered X-rays, which raises concerns about whether this exposure might harm thyroid function or increase the risk of thyroid disorders.
The thyroid gland is sensitive to ionizing radiation because it is a small, highly vascular organ that actively absorbs iodine, a process that can also lead to the uptake of radioactive or scattered radiation. Studies have shown that workers who are regularly exposed to scattered radiation in CT scan rooms have a higher probability of developing thyroid gland disorders, especially if their exposure is prolonged over many years. This suggests that repeated or chronic exposure to scattered radiation, even at low doses, can affect thyroid hormone levels and potentially lead to dysfunction or disease.
However, for patients undergoing a typical CT scan, the radiation dose to the thyroid is generally low and brief. The risk of thyroid damage or dysfunction from a single CT scan is considered minimal. Modern CT scanners and protocols aim to minimize radiation exposure by optimizing the dose and shielding sensitive organs like the thyroid when possible. Despite this, the thyroid remains one of the more radiosensitive organs, and cumulative radiation exposure from multiple scans or other sources can increase risk.
Radiation can cause damage to thyroid cells by inducing DNA damage or altering the function of thyroid hormone-producing cells. This can lead to hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), or in some cases, increase the risk of thyroid nodules or cancer. The risk is higher in children and young adults because their thyroid tissue is more sensitive to radiation.
In medical practice, radioactive iodine (I-131) is deliberately used to treat thyroid conditions such as hyperthyroidism and thyroid cancer by destroying overactive or malignant thyroid cells. This treatment demonstrates that radiation can significantly impact thyroid function, but it is a controlled and targeted use of radiation with therapeutic intent.
In summary, while the scattered radiation from CT scans can theoretically affect the thyroid gland, the risk to thyroid function from a single or occasional CT scan is very low. The main concern lies with repeated or occupational exposure to ionizing radiation, which can increase the likelihood of thyroid dysfunction or disease. Protective measures, such as thyroid shielding and limiting unnecessary scans, are important to reduce this risk. Patients should discuss any concerns about radiation exposure with their healthcare provider, especially if they require multiple imaging studies involving the neck region.