Answer to Question #2369 Submitted to "Ask the Experts"

Q

I am an x-ray technician. I have currently been having some trouble that they think may be my thyroid. I have all of my radiation levels from my film badge, but I wondered what levels become dangerous to the thyroid. Also, what type of effects could it cause in the thyroid?

A

Available data indicate that the thyroid gland in children is among the most sensitive organs in the body to a radiation-induced tumor, both benign and malignant. There appears to be no threshold dose for this effect. Some older studies have found an increased incidence in thyroid tumors in children following doses as low as 60 mGy (6 rad) or thereabouts. This high sensitivity seems to disappear during adolescence. The adult thyroid is much less sensitive. A search of the National Library of Medicine bibliographic Web site found 12 papers published on the subject of occupational radiation exposure and thyroid tumors. The most recent is by Sont et al, Am J Epidemiol. 2001 Feb 15;153(4):309-18. The problem with these studies is the long latent period between radiation exposure and appearance of a detectable tumor. Thus, all positive findings are related to exposures that occurred decades ago, when occupational exposures were much greater than they are now. We will not know for several decades whether current doses are harmful or not.

Conclusion: If your thyroid problem is related to a tumor, either benign or malignant, then the probability is small but not zero that it might be related to your radiation exposure history. If, on the other hand, your problem is not related to a tumor, then it almost certainly is not related to your occupational exposure.

S. Julian Gibbs, DDS, PhD