Farmin Shahabuddin, MPH and Akashleena Mallick, MD, MPH, Cancer Prevention and Treatment Fund
Thyroid cancer diagnoses have increased dramatically in recent years, and experts are asking why. The good news is that doctors now use better imaging tests that can find very small thyroid tumors. The bad news is that some of these very small tumors might never cause health problems even if they are not treated.
Another possible reason for the increase in thyroid cancer could be because radiation was commonly used for minor childhood issues decades ago, such as swollen tonsils and acne. This resulted in a surge of thyroid cancer when those children became adults. More recently, experts have looked at whether repeated exposure to medical imaging tests that use radiation, such as CT scans, dental X-rays, and other scans, might also increase the chance of thyroid cancer over time. Fortunately, medical imaging today uses less radiation than it did in the past due to improved technology1, and the use of lead aprons and other protections has further reduced exposure.
In this article, we will let you know what the most recent research shows and what you can do to reduce any added chance of thyroid cancer caused by X-rays, CT scans, or other medical scans, or other radiation, while still getting the care you need.
The thyroid is a small, butterfly-shaped gland in the front of the neck. It is just below your Adam’s apple, although the latter may not be visible. The thyroid makes hormones that help regulate metabolism, heart rate, blood pressure, and body temperature. Since the thyroid sits close to the surface of the skin, it is sensitive to radiation.2 For more on the gland and how cancer develops there, see our thyroid cancer article here.
What Is Radiation in Medical Imaging?
Radiation can come from sunlight or from human-made sources like medical imaging. Thyroid cancer can develop from many sources of radiation, such as past cancer treatment to the head or neck, nuclear accidents, and workplaces that use radioactive materials. For more information, see Everything You Ever Wanted to Know About Radiation and Cancer but Were Afraid to Ask.
In medicine, X-rays are the most common form of radiation used to take pictures inside the body. Other tests using radiation that we will discuss in this article include X-rays of the head and neck, CT scans, dental X-rays, dental CT scans, and mammography. Each test uses a different amount of radiation, and some tests expose the thyroid to more radiation than others. When imaging is done close to the thyroid (as described later in this article), patients can ask for a ‘thyroid shield’ as described below, which is a lead cover placed over the neck to keep radiation from reaching the thyroid.
Radiation and Thyroid Cancer in Children and Women
In 2023, about 2.5 million CT scans were performed on children in the U.S. A study projected that the radiation from these scans would eventually lead to about 3,500 cases of thyroid cancer in those children.3 The thyroid is particularly sensitive to radiation during childhood and adolescence, when the gland is most active. Cells in the thyroid divide more rapidly in younger patients, and children have more years ahead in which a cancer could develop.1 For these reasons, parents and caregivers may want to ask their doctors whether a test without radiation could be used instead.
Women are also more sensitive to radiation from imaging, which may help explain why thyroid cancer is diagnosed three times more often in women than men.4 The reasons are not yet completely understood. For more on women and thyroid cancer, see our thyroid cancer article here.
X-rays
Regular X-rays of the head, neck, chest, or upper spine deliver a small amount of radiation to the thyroid, though usually much less than a CT scan. For most patients, a single X-ray carries a small added chance of thyroid cancer.1 Repeated X-rays of the same body part over many years can increase the chance of thyroid cancer over time.
Before an X-ray, it is reasonable to ask whether a recent image on file, or a test without radiation, could give the same information. For X-rays of areas close to the neck, a thyroid shield can be requested to help reduce exposure to the thyroid.1
CT scans
A CT scan takes many X-ray pictures from different angles to combine them into a detailed image. As a result, a CT scan delivers more radiation than a regular X-ray. CT scans of the head, neck, chest, and upper spine expose the thyroid to the most radiation since the thyroid gland is located close to those areas of the body.2
When a CT scan does not include the neck itself, a thyroid shield can be helpful in lowering exposure to the thyroid, and patients can ask their healthcare professional whether one can be used.1
Before a CT scan, it is reasonable to ask your healthcare professional:
- Is the scan truly needed?
- Could a test without radiation, such as an MRI or ultrasound, give the same or better information?
- Can a thyroid shield be used to protect the thyroid when the scan does not include the neck?
Dental CT scans
Cone beam CT (CBCT), also known as a dental CT scan, is a newer scan that uses X-rays to take 3-D pictures of the teeth, jaw, and sinuses. Dentists may use it before braces, dental implants, or jaw surgery. CBCT delivers much less radiation than a medical CT scan, but more than a regular dental X-ray. Some of this radiation can reach the thyroid when the scan includes the lower jaw.5
In February 2024, the American Dental Association (ADA) updated its guidance to no longer recommend the routine use of thyroid shields during dental imaging, including CBCT, because the shield can block part of the image and lead to a repeat scan, which means more radiation overall.7 The ADA notes that modern equipment and restricting the size of the X-ray beam protect patients more effectively than a shield does. A patient who prefers a shield can still request one, and the dentist should consider whether using one would increase the chance of needing a repeat scan.7
Dental X-rays
Previous concerns about dental X-rays mostly came from studies of machines used before 1970, when the equipment delivered more radiation than today’s machines. Today, dental X-ray technology has improved, and many dental offices use digital sensors that lower radiation exposure even further. Due to these changes, a 2025 review found that current evidence does not clearly show that modern dental X-rays increase a person’s chance of developing thyroid cancer. ⁷ However, dental X-rays should still be used only when they are needed for diagnosis or treatment.
Mammograms
A mammogram is an X-ray of the breast.8 Since breasts are far from the thyroid gland, the chance of a 40-year-old woman developing thyroid cancer from one mammogram is about 6 in 1 billion. Even with yearly mammograms from age 40 to age 80 (which is more frequently than is recommended), the chance of developing thyroid cancer remains extremely low, about 1 in 18 million.9 That is why thyroid shields are not recommended during a mammogram.
The Bottom Line
CT scans expose the thyroid to more radiation than dental X-rays, dental CT scans, mammograms, and X-rays. However, the chance of thyroid cancer increases with the number of scans. Children, adolescents, and women are more sensitive to medical imaging radiation, so extra care is needed. For medical X-rays and CT scans of areas close to the neck, a thyroid shield can be requested. For dental X-rays, dental CT scans, and mammograms, current guidance does not recommend a thyroid shield for routine use, since it can interfere with the image and require a repeat scan. However, to reduce exposure to radiation, it makes sense to ask your doctor whether a scan is truly needed and weigh the benefits against the harms.
References
- American Cancer Society. (2026, April 23). Understanding radiation risk from imaging tests. https://www.cancer.org/cancer/diagnosis-staging/tests/imaging-tests/understanding-radiation-risk-from-imaging-tests.html
- Saenko, V., & Mitsutake, N. (2024). Radiation-related thyroid cancer. Endocrine Reviews, 45(1), 1–29. https://doi.org/10.1210/endrev/bnad022
- American Thyroid Association. (2025, September). Do CT scans increase the risk of thyroid cancer? Clinical Thyroidology for the Public, 18(9), 5. https://www.thyroid.org/patient-thyroid-information/ct-for-patients/september-2025/vol-18-issue-9-p-5/
- Cao, C.-F., Ma, K.-L., Shan, H., Liu, T.-F., Zhao, S.-Q., Wan, Y., Zhang, J., & Wang, H.-Q. (2022). CT scans and cancer risks: A systematic review and dose-response meta-analysis. BMC Cancer, 22, 1238. https://doi.org/10.1186/s12885-022-10310-2
- Lai, S. T. T., & Bauer, A. J. (2025). Approach to the pediatric patient with thyroid nodules. The Journal of Clinical Endocrinology & Metabolism, 110(8), 2339–2352. https://doi.org/10.1210/clinem/dgaf090
- Yeom, H. G., Kim, J. E., Huh, K. H., Yi, W. J., Heo, M. S., & Lee, S. S. (2022). Impact of thyroid gland shielding on radiation doses in dental cone beam computed tomography. Oral Surgery, Oral Medicine, Oral Pathology and Oral Radiology, 134(6), 801–812. https://doi.org/10.1016/j.oooo.2022.05.005
- Holmström, L., Tranæus, S., Hultin, M., Mejare, I., Kadesjö, N., & Shi, X.‑Q. (2025). Negative health effects of dental x‑rays: A systematic review. Acta Odontologica Scandinavica, 84, 328–340. https://doi.org/10.2340/aos.v84.43673
- Centers for Disease Control and Prevention. (n.d.). About mammograms. U.S. Department of Health and Human Services. Retrieved April 28, 2026, from https://www.cdc.gov/breast-cancer/about/mammograms.html
- Stempniak, M. (2022, February 10). Misinformation on mammography thyroid shielding goes viral, presenting opportunity for radiologist clarification. Radiology Business. https://radiologybusiness.com/topics/medical-practice-management/mammography-thyroid-shielding-radiologist