Answer to Question #7303 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
I would like to know the dose limit to the thyroid gland. I know the thyroid is a radiosensitive organ. What is the limit for the dose that a thyroid gland can receive during any diagnostic examinations (e.g., CT)?
Thank you for your question. Actually, the adult thyroid is very insensitive to radiation exposure. It appears, in fact, that the risk of thyroid cancer in someone over the age of 20 exposed to radiation is either zero or too small to measure (NAS 2006).
There is no limit on the amount of radiation exposure for a patient undergoing medical diagnostic exams. This is because the patient and his/her physician should be assuring the exams are justified and beneficial to the patient.
For someone occupationally exposed (like an x-ray technologist), the annual limit to the thyroid is 50 rem (rem is a unit of effective radiation dose). For occupationally exposed individuals who might receive higher thyroid doses, we try to limit their exposure by the use of leaded thyroid collars.
Certified Medical Health Physicist
National Academy of Sciences (NAS). Health effects from exposure to low-level ionizing radiation BEIR VII Phase 2. Washington, DC: National Academies Press. 181-182; 2006.