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Dental X-Rays linked to Brain Tumors (washingtonpost.com)
79 points by ck2 1745 days ago | hide | past | web | 25 comments | favorite

The study found at a general level that people with meningioma were more than twice as likely as people without the brain tumor to have had a bitewing X-ray sometime in their life.

Running a story like this using relative percentages, but no absolute values, is absurd and contemptible.

I'm not finding any absolute values for meningioma rates in any other stories about this particular study, but old pal wikipedia says:


Many individuals have meningiomas but remain asymptomatic (no symptoms) for their entire life, so the meningiomas are not discovered until after an autopsy. 1-2% of all autopsies reveal meningiomas which were unknown to the individuals during their lifetime, since there were never any symptoms. In the 1970s, tumors causing symptoms were discovered in 2 out of 100,000 people, while tumors discovered without causing symptoms occurred in 5.7 out of 100,000, for a total incidence of 7.7/100,000. With the advent of modern sophisticated imaging systems such as CT scans, the discovery of asymptomatic meningiomas has tripled.

I think I'll worry about something else.

Thanks for this; I was about to say pretty much the same thing.

Gerd Gigerenzer has a nice book about the way risk is communicated.



Otis Brawley's "How We Do Harm" is also good reading.

You don't feel 40 to 90 percent higher risk from bitewings is statistically significant?

Statistically significant yes. But 90 percent more of 0.00002 is 0.000038. It would be like avoiding conductive jewelry because you're worried about lightning.

You added the word "statistically". I know people tend to kvetch about statistical significance almost reflexively, but that's not being done here. I believe the implication here is that it just plain isn't worth worrying about.

Not to mention, cavities and other dental problems pose a measurable threat to your health and longevity (not to mention quality of life), so I would bet a certain amount of radiation risk can actually be offset by the resulting improved dental health.

That's the wrong question. The question is if the X-rays are actually necessary in order to have good dental health, and apparently the answer is no.

Dentists use them because "what's the harm", but now that a harm is demonstrated they should use them only when actually necessary (when "the benefit outweighs the risks").

Um, a dentist's time isn't infinite, and other methods of examination can be more annoying for the patient than an x-ray. I guarantee you that if we don't use x-rays then in practice people are going to suffer more from dental issues.

If a tumour is only discovered in an autopsy, it's not clinically significant... and the benefits of the x-rays may well outweigh the risk of such a (in this case, usually benign) tumour.

Definition per http://www.ncbi.nlm.nih.gov/books/NBK10468/ :

"Clinically significant: A result that is large enough to affect a patient’s disease state in a manner that is noticeable to the patient and/or caregiver."

But "autopsy" means the person died but not when they died. So an autopsy of a person killed by gunshot in their 20's doesn't alters the average lifetime risk from the xrays.

If it has the capacity to produce one kind of cancer then it has the capacity to produce a kind of cancer that was not part of the study.

What is absurd and contemptible is an attitude that "if such and such medical intervention was not proven to cause harm, then we should act as if it does cause no harm", ignoring the fact that the law of unintended consequences trumps what medical science has not yet proven.


Now just imagine the proof in 20 years about TSA radiation exposure.

The lawyers will get billions, the victims will get $20, while the taxpayers get to pay for the machines now and the settlement later.

haha, no.

A law would be passed removing the ability to sue the TSA for giving you cancer.

To put various radiation exposures in perspective (not entirely certain of the validity of the link, it doesn't cite sources):


>A typical dental x-ray image exposes you to only about 2 or 3 mrem. The National Council on Radiation Protection (NCRP) says that the average resident of the U.S. receives about 360 mrem every year from background sources. This comes from outer space, radioactive materials in the earth, and small amounts of radioactive material in most foods we consume.

>Some typical sources that may expose you to radiation also include smoke detectors (less than 1 mrem per year), living in a brick house instead of a wood one (about 10 mrem per year due to radioactive materials in the masonry), cooking with natural gas (about 10 mrem per year from radon gas in the natural gas supply), reading a book for 3 hours per day (about 1 mrem per year due to small amounts of radioactive materials in the wood used to make the paper), and even from flying in an airplane (about 5 mrem for one cross-country flight because of the increased altitude.)

Radiation concentrated in one place (such as with xrays) is a lot more harmful than general radiation.

Yep, I agree. I just wanted to put up a list of common exposures so people have some bearing on the level of radiation that we are talking about :)

Some perspective from XKCD: http://xkcd.com/radiation/

In the study, people were asked if they remembered having such an X-ray any time during their life. And people who had a brain tumor were more likely to answer yes.

I wouldn't be surprised if that just means that people are likely to forget about such exams, unless they get a brain tumor and start fretting about what might have caused it. Maybe they'll even start "remembering" radiation exposure in their youth that never actually happened. The study itself may produce such false memories by suggestive questioning.

I'll take note if the link can be shown with real data rather than questionnaires. Until then, I'm sceptical.

I think I just had one of these done in 2011. Nice to have more fuel for my hypochondria fire.

"The exposures to dental X-rays in the study took place in the 1960s, when dental X-rays delivered higher doses of radiation than today’s do."


The lowest radiation doses for dental x-ray are from modern digital systems, so if you care, it might be worth asking your dentist if he would upgrade. (The digital ones also give better images, are easier to work with if you need to send the x-ray offsite, etc.

This particular cancer is probably a non-risk, but there are a lot of reasons to go digital.

Does anyone know how much lower the doses are from modern dental x-rays compared to the ones several decades ago which make up most of the study? Is it a difference of 20%, or a factor of 20?

I thought this would add another interesting wrinkle to the conversation. It is from a few years ago, but I found it counterintuitive and interesting (as a lay reader).

"The safety of routine X-rays has been called into question following the unexpected discovery that cells exposed to low doses avoid or delay repairing damaged DNA."


If only I could use this as my excuse for "missing" the dentist these past couple years...

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