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March 30th, 2011
06:16 PM ET

Does radiation from dental X-rays cause thyroid cancer?

Every weekday, a CNNHealth expert doctor answers a viewer question. On Wednesdays, it's Dr. Otis Brawley, chief medical officer at the American Cancer Society.

Asked by Cate, Kennesaw, Georgia

I have heard that there is an increase in the number of people getting thyroid cancer. Is this true and is radiation from dental X-rays a cause for the increase?

Expert answer:

Dear Cate,

The thyroid is a gland in the neck below and in front of the throat. It secretes hormones that control metabolism. People with low thyroid function gain weight and are lethargic. Those with an overactive thyroid have weight loss and can experience nervousness and other problems.

The American Cancer Society estimates that 44,670 new cases of thyroid cancer occurred in 2010 (33,930 in women, and 10,740 in men). Thyroid cancer caused about 1,690 deaths (960 women and 730 men). Thyroid cancer is different from many other adult cancers in that it is commonly diagnosed in younger people. Nearly two of three cases are found in people between the ages of 20 and 55.

The chance of getting thyroid cancer has risen in recent years. In the U.S., there has been a rise in the age-adjusted incidence rate of diagnosed thyroid cancer since 1980. The rate for women went from 6 cancers per 100,000 American women in 1980 to 17 per 100,000 American women in 2007. The comparable rates of diagnosis for men went from 2.5 per 100,000 in 1980 to 5.8 per 100,000 in 2007. Even with a near tripling of the female incidence rate in the past 30 years, it is small compared with the cancer rates for lung, colon, breast or prostate cancer.

Despite these changes in incidence rates, risk of death has remained stable over the past 30 years. It has been at about 0.5 deaths per 100,000 American women and at 0.4 to 0.5 per 100,000 for American men. Indeed, thyroid cancer is one of the most survivable of cancers. More than 97% of patients do very well.

Much of this increase is thought to be the result of the increased medical imaging of the thyroid. It is not so much that there are more thyroid cancers, as that more thyroid cancers are being discovered or diagnosed. Use of CAT scans, MRI scans and thyroid ultrasound has dramatically increased over the past 30 years. These tests can detect very small thyroid nodules that several decades ago would not have been found.

I know it is hard to imagine that there are some cancers that are not clinically significant, meaning cancers of no threat that do not need to be treated. This is the case in some thyroid cancers, some prostate cancers and in several other malignancies. One of medicine's great problems is we can diagnose a cancer, but we cannot accurately predict those who need therapy and those who do not. Therapy for thyroid cancer is most commonly surgical removal of half or all of the thyroid.

While small cancerous thyroid tumors of no threat to health are being found, a part of the rise in thyroid cancer incidence is due to finding an increased number of larger cancerous tumors that are clinically significant.

Radiation exposure does increase risk of thyroid cancer, and the risk increases with the amount of radiation exposure. The developing thyroid is especially susceptible to radiation. Children exposed to radiation are at increased risk of developing thyroid cancer later in life. The thyroid can absorb radiation through ingestion of radioactive material, especially radioactive iodine, or through external exposure such as from an X-ray machine.

The National Cancer Institute has done a study to see if the rise in thyroid cancer incidence is related to radioactive iodine released during aboveground nuclear weapons testing, which was common in the western U.S. from 1945 to 1963. The conclusion is that the rise is not related. Most of those affected by the increase in incidence were born years after nuclear testing stopped.

Dental X-rays give a very low dose of radiation to the mouth. There is some scatter of radiation and the potential for some radiation absorption by the nearby thyroid and other organs. The American Dental Association notes that a leaded apron placed over the torso minimizes radiation exposure to the chest and abdomen and should be used when any dental X-ray is taken. The group also notes that a leaded thyroid collar can protect the thyroid from radiation and should be used whenever possible.

While the experts that I consulted do recommend use of a thyroid collar, none of the experts was especially worried that dental X-rays are a significant cause of thyroid cancer. There is however significant concern that radiation from other forms of medical testing may be causing some thyroid cancers. CT scanning is the medical procedure that concerns experts the most. It uses higher levels of radiation than conventional X-rays and much higher levels of radiation than are used in dental X-rays.


soundoff (29 Responses)
  1. Alex

    One thing to note is cone beam CT technology is being used in dentistry right now, especially by oral surgeons. The newer cone beam technologies have effective dose rates that are equal to or lower than conventional dental x-rays, namely d-speed film so the amount of exposure to the thyroid, salivary glands, etc. is very low. As a patient, I will not go to a dentist who does not have digital x-rays or cone beam technology if I need that kind of service. I am not a dentist, but dental radiology has really come a long way to decrease doses with digital x-rays and cone beam ct. I just wish other CT technologies, namely for the torso, brain, etc. would see some kind of improvement in dose reduction and MRI and ultrasound start to be used for procedures that CT is now used for. I know there was a study done in Quwait last year that found an increase in thtroid cancers from dental x-rays but I also learned that it was an amazingly flawed study.

    March 30, 2011 at 20:39 | Report abuse | Reply
    • Jeff

      Alex, as a practicng dentist, I can tell you that the D-speed film that you mentioned hasn't been the standard type of conventional film used in dentistry in well over a decade. E speed film was the standard of care, and the big difference between D and E speed film is that less radiation is needed to expose the film with E speed than D speed. Further off, nowadays an ever growing percentage of dental offices have switched to digital x-ray systems, and when I made the switch in my office a few years back now, on the the key things that the manufacturers rep told us, is that we can further cut the amount of radiation needed to expose the digital x-ray in half over what we were using for E speed film before

      March 31, 2011 at 09:03 | Report abuse |
  2. Laura

    Of course, they now like to x-ray kids twice a year......I wonder if this is an issue.

    March 30, 2011 at 20:45 | Report abuse | Reply
    • -annonymous

      I am almost 40 and when I was a child my parents would almost never let the dentist give me xrays (with the exception of a cavity and braces). I can probably count on one hand the times I've had xrays at the dentist. At the time there were studies that thought it could interfere with normal growth in general. It's really not necessary if you teach your kids how to take care of their teeth. I still decline xrays now and the dentists really hate it but hey it's my health. My teeth are fine.

      March 30, 2011 at 21:46 | Report abuse |
    • D3

      why would you xray a kid twice a year if the kid was cavity free for 3 or more years. but this is not uncommon if the kid is prone to getting new cavities.

      May 26, 2011 at 01:28 | Report abuse |
  3. Sasha

    I am a 2 time thyroid cancer survivor. As a patient, I can tell you it's very frustrating having this illness and not knowing how I got it. I will now insist on protecting my young son's neck area at his dentist appointments for xrays. I don't want anyone to have to go thru this type of illness.

    March 30, 2011 at 21:42 | Report abuse | Reply
  4. Shane

    What about the newer (completely unnecessary) "panoramic" dental x-rays that expose the patient to hundreds of times more radiation than traditional x-rays? It's very odd the author did not mention these.

    March 30, 2011 at 22:14 | Report abuse | Reply
    • Alex

      Which ones are you refering to...cone beam ct or 3D volumetric scanning? I have had a very chronic and frustrating dental pain condition for well over three years and have had so many x-rays to my mouth it is ridiculous and I may(and probably will have more) down the line...nothing I can really do about it but try and take care of my condition. I actually met with a dental radiologist, someone who is very knowledgable in radiation and dental x-ray doses and he did mention to me that many of the new technologies that are being used more and more are not hundreds of times more, but maybe 6 – 8 times more, sometimes even less than traditional x-rays. I t depends on the type of study. I had one cbct scan done of two teeth and it was equivelent to 1 or two d-speed traditional x-rays...very low in general; however, I will only submit to any x-ray if it is completely justified and refuse one if it is not.

      March 30, 2011 at 22:30 | Report abuse |
    • nkil

      I am a pediatric dentist, and I can't tell you the number of times we have detected some type of pathology (cancerous and non-cancerous) that would never had been detected without taking a "completely unnecessary" panoramic dental x-ray.

      March 31, 2011 at 09:02 | Report abuse |
  5. robyn

    shane, as a hygienist im wondering where you got your information regarding pans? its completely inaccurate. google can hook you up with a little more info...

    March 30, 2011 at 22:25 | Report abuse | Reply
  6. CHeryl

    Over the last year I was diagnosed with Grave's Disease. I have a hard time believeing it happened spontaneously and have tried to put my finger on what triggered it. I can't help but wonder if some of the somewhat major (I think) dental work I had done (tooth pulled and a bridge put in) could have had a role. Between x-rays and numbing shots and overall stress to my mouth area, I don't rule anything out. Until the doctors can come up with a reason on what actually causes the thyroid to overact/underact (more research...anyone??), don't tell me that something unequivocably doesn't cause it.

    March 30, 2011 at 22:28 | Report abuse | Reply
    • Web MD

      I can tell you, unequivocally, that bridge work does not cause Grave's disease.

      March 31, 2011 at 10:35 | Report abuse |
  7. Kelcy

    My daughter had thyroid cancer at 23 which was almost ten years ago. She had had a goitered thyroid for three or four years before it was removed for that reason (goiter). Eighteen months before that her thyroid had been biopsied to ensure it was inflammatory goiter and not cancer. No cancer was present at that time. Yet when it was removed the cancer was huge and was "on the margin" meaning there was cancerous tissue up against clean, non-thyroid tissue. We were lucky to have had it removed then or else it would likely have spread by the time other symptoms cropped up.

    She had not had more than the regular once a year dental x-rays throughout her life up. However, after her cancer was discovered it became a topic of discussion at my office and found out some interesting information. In my office of 50 people 10 of us (me included) had dysfunctional thyroids in the prior 20 yrs. We were in the 30-50 yr old age range at the time and had the problem occur in our 20's and 30's (mine was at 32). One of those (a male) had thyroid cancer. We were clearly prior to what this article considers a recent increase in the cancer rate.

    I wonder less about dental x-rays and more about what is going on environmentally that is making thyroid cancer so prevalent. Most began as goiters as did my daughters. And FYI to the readers.... when the goiter first occurred research on it did not pop up with cancer. However, thyroid cancer popped up with over 50% of goiters becoming cancerous.

    March 30, 2011 at 23:34 | Report abuse | Reply
  8. Steve - Dallas

    I have an under-active thyroid, and I had two cats who both developed thyroid tumors in middle age. I'm wondering if there are environmental causes that haven't been determined yet. Of course, I've had my share of dental x-rays, and one CT scan.

    March 30, 2011 at 23:52 | Report abuse | Reply
  9. Jennifer

    Of course they do x-rays once or twice a year on children. They are no longer doing preventative fillings in every molar that are made of mercury. X-rays catch cavities early enough to retain the most natural tooth structure during the restorative process, which means walking around with less potentially harmful materials in your mouth (hey, even the white composite filling material has chemicals in it I, as a dental assistant, do not want constant exposure to). X-rays can detect possible infection in a tooth that does NOT have any cavities before you are in dire pain on a Saturday night. And believe it or not, it's actually really important to see what the teeth are doing below the gum line, particularly in children. My son recently had what I thought to be a minor injury to his mouth – it resulted in an immediate extraction to prevent injury to the developing permanent tooth and prevent an almost certain infection just inches from his brain (and yes, people do die from these things). And concerning the levels of radiation... who has been to the beach for a few hours in the last year? Or sat too close to your TV for a movie? You just got more radiation than a set of dental x-rays.

    Cheryl, my mother has an autoimmune disease that flared up from a surgery on her shoulder. Your Grave's disease probably would have done the same thing if you had some sort of work done on any other body part. It probably wasn't specifically the dental work itself as much as general stress to the body. If you were stressed about the procedures or the financial aspect, that could have an impact too – stress is widely known to agitate autoimmune diseases. I've had many patients with a variety of autoimmune diseases who have had extensive dental work done (autoimmune patients tend to have a fair amount of dental problems from the disease) and they were fine.

    One thing I find interesting about this discussion is how everyone is viewing this "increase in thyroid problems" discussion from the patient's POV. "I had 3 sets of x-rays done so my thyroid problem is because of that". Dental professionals are constantly exposed. As an assistant, I get patients that won't hold still or gag before you even get the film in their mouth and you have to hold it with your finger. Or you don't have a safe distance to stand, or my favorite... the button not being 6 feet away or behind a wall. Patients go through a set every couple of years where professionals get constant exposure. I don't see any concern for the professionals.

    March 31, 2011 at 00:20 | Report abuse | Reply
    • Shanon

      Jennifer

      I don't know where you get that sitting in the sun exposes you to any more penetrating radiation than being indoors. On the beach you'd get UV radiation which doesn't penetrate the dermis so would definately not be responsible for increasing the chance of thyroid cancer and I don't know what you're implying regarding sitting too close to the TV....poor examples because they are in no way comparable to x-radiation. (space sourced Gamma and Beta radiation maybe but I'm getting the same amount of that sitting inside my house as out on the beach since it's so penetrating).
      Your comments are inaccurate and hopefully for your sake and your patients sake, you do some reading about radiation biology.

      April 18, 2011 at 17:27 | Report abuse |
  10. SAM

    Radiation in any form is dangerous,Just Like ALCOHOL

    March 31, 2011 at 03:53 | Report abuse | Reply
  11. Teresa

    I have and underactive thyroid also. We also get the same song and dance "the sun gives you just as much radiation". My parents and I constantly tell the dentist we DO NOT WANT X-RAYS!!! They in turn tell us it is needed. We know better it is like a sales pitch for the office to bilk our insurance companys for more money!!! I have not had a cavity in over 20 years!!! They are relentless with my child getting x-rays also. They once x-rayed her and said they found a cavity. We went back a couple weeks later to get it filled. Only to find that cavitiy was no longer there??? Beware these dentist want to get ALL the Insurance money they can out of you!!! There should be a law against pressuring patients into doing having a procedure done that they do not want!! I have wanted to leave my dentist office due to this.

    March 31, 2011 at 09:13 | Report abuse | Reply
    • SalBelle

      I did leave my dentist because she insists on regular xrays, whether you need them or not. I discussed it with her, and their stance is, either submit to radiation to satisfy insurance requirements or leave. I don't lrespond well to bullying, so I left.

      September 13, 2011 at 14:40 | Report abuse |
  12. marc gunn

    Dentists always downplay this but the reality is they aren't physicists or MDs. (i've heard some comparing it to sunlight, which isn't a good comparison because UV doesn't penetrate deeply.) What is known is the thyroid gland is VERY sensitive to radiation, and even if dental x-rays are low they are concentrated near the thyroid gland. Thyroid disorders are HUGE in the United States, and this article fails to give a true magnitude of the disorder. Millions of people are dysthyroid and ultimately have it removed or ablated and take synthroid. We really need to know why.

    March 31, 2011 at 10:21 | Report abuse | Reply
    • Kathryn Weaver

      I think read that fluoride is very bad for the thyroid gland, and the United States is big on drinking water fluoridation. See the connection?

      March 31, 2011 at 10:42 | Report abuse |
  13. Lindalou

    Anything unnatural, radiation, chemicals, toxins in the air were not meant to be put into the human body. Why they insist on regularly radiating us for dental xrays is beyond me. Yes if I'm having a problem and its not apparent visibly fine, do it. But as a regular exam..no way. To purposely expose ourselves to a known carcinogen is trouble. Why do you think they step out of the room if its so safe.

    March 31, 2011 at 10:55 | Report abuse | Reply
  14. Nancy

    answer- yes, they can cause cancer. Wear a lead protector.

    March 31, 2011 at 11:56 | Report abuse | Reply
  15. Captain_Colossal

    the price we pay. no way around it really. unless you wanna pay for a CT scan or something.

    March 31, 2011 at 18:28 | Report abuse | Reply
  16. ed Bailey

    The person who doesn't think that environmental toxins are HEAVILY influencing our health negatively IS A FOOL!

    April 2, 2011 at 04:07 | Report abuse | Reply
  17. Reality Check

    "And concerning the levels of radiation... who has been to the beach for a few hours in the last year? Or sat too close to your TV for a movie? You just got more radiation than a set of dental x-rays."

    Your TV does not produce ionizing radiation. It is truly frightening that you don't understand that difference.

    April 2, 2011 at 17:20 | Report abuse | Reply
  18. how to generate income

    Thanks for the good writeup. It actually was a entertainment account it. Look advanced to more delivered agreeable from you! By the way, how could we keep in touch?

    May 15, 2012 at 17:55 | Report abuse | Reply
  19. A

    Good answer,very clear, i feel better now. Thank You.

    December 16, 2012 at 22:07 | Report abuse | Reply
  20. JR

    And, if you go for a panoramic x-ray, and the technician, or the machine seem 'off' – leave immediately. Do not think you have to "behave."

    February 17, 2013 at 21:58 | Report abuse | Reply

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