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How Risky are CT Scans?

February 13, 2014 by Michael Greger M.D. in News with 29 Comments

Cancer Risk from CT Scan Radiation

The greatest radiation exposure risk comes not from the Fukushima fallout or the polonium naturally found in all seafood (see my last video, Fukushima and Radioactivity in Seafood), but from doctors.

This was the study that originally shook things up: “Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CAT scans.” Researchers concluded that the best available risk estimates suggest that pediatric CAT scans (also known as CT scans) will result in significantly increased lifetime radiation risk. How increased? In the United States, of the approximately 600,000 abdominal and head CT scans annually performed in children under the age of fifteen, 500 of these individuals might ultimately not just get cancer but die from cancer attributable to the CAT scan radiation. In response to this revelation, the editor-in-chief of the leading radiology journal admitted that radiologists have not been watching out for children.

The cancer estimates were based on data from Japanese atomic bomb survivors, in terms of how many deaths one can expect from what kind of radiation dose. However, there’s never been a study able to actually document the excess cancers—until now. It turns out that the X-rays released by CAT scanners may be twice as carcinogenic as the higher energy gamma rays released from atomic bombs. Just a few CT scans may triple the risk of brain tumors and leukemia in children.

Other studies are being performed around the world to quantify the risk and should be out in the next few years. Until then, what can we do? First of all, we should get X-rays only when absolutely necessary. Good evidence suggests that between a fifth and a half of CAT scans aren’t necessary at all—they could be replaced with another type of imaging or not performed at all. That’s a lot of added cancer risk for no added benefit.

If you check out my 4-min video Cancer Risk From CT Scan Radiation, you can see the risk of developing cancer for different groups after getting one CT scan. The risk of developing cancer after a single CT scan may be as high as 1 in a 100 for a baby girl. It can take years for cancer to develop, though, which is why the risk is lower in the elderly since they have fewer years left to live. The diagnostic medical radiation dealt out in one year is estimated to cause 2,800 breast cancers among women in the United States, and 25,000 other cancers. That’s doctors causing a lot of cancer.

One chest CT scan is like getting 400 chest X-rays, and a stress test heart scan can be like getting over a thousand X-rays. Doctors need to communicate the risks of these procedures, using relatable analogies. For example, the risk of a chest CT is like the risk of having a car crash during 2500 miles of highway driving or of smoking 700 cigarettes. You pick up a pack of cigarettes and there’s a warning label, but then you go in for thallium heart scan, and no one minds telling you that the risk corresponds to smoking 1400 cigarettes. One in every 270 middle-aged women that get an angiogram may get cancer because of that one test.

The risk associated with the thallium heart scans shocked me. By eating healthy, we may not only eliminate the death and disability associated with heart disease and its treatment (such as open heart surgery), but the risks associated with heart disease diagnosis as well. See these videos for my advice on preventing heart disease:

As I explain in my full-length live presentation on preventing, arresting, and reversing the 15 top killers (Uprooting the Leading Causes of Death), adverse drug reactions from prescription drugs are estimated to cause more than 100,000 deaths in the United States every year, making doctors the sixth leading cause of death. And that’s not counting other “iatrogenic” (physician-caused) harm, such as these radiation risks or medication errors or infections acquired in hospitals. My profession needs to do a better job of offering fully informed consent, clearly and comprehensively explaining the risks and benefits of each alternate course of action.

What about getting X-rays at the dentist? I’ve got a video about that too: Do Dental X-Rays Cause Brain Tumors?. And cell phone radiation? See my video Do Cell Phones Cause Cancer?

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live year-in-review presentations Uprooting the Leading Causes of Death and More Than an Apple a Day.

Image credit: thesmokingsection / Flickr

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Dr. Michael Greger

About Michael Greger M.D.

Michael Greger, M.D., is a physician, author, and internationally recognized professional speaker on a number of important public health issues. Dr. Greger has lectured at the Conference on World Affairs, the National Institutes of Health, and the International Bird Flu Summit, testified before Congress, appeared on The Dr. Oz Show and The Colbert Report, and was invited as an expert witness in defense of Oprah Winfrey at the infamous "meat defamation" trial. Currently Dr. Greger proudly serves as the Director of Public Health and Animal Agriculture at the Humane Society of the United States.

View all videos by Michael Greger M.D.

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  • Monty1

    Thanks very much for the informative posts! But you keep referring to eliminating death from heart disease and the like–but, of course, even if everyone ate a maximally healthy diet we would still not live forever and we wouldn’t all die solely from accidents, but also of disease. I assume that you’re talking just about premature, preventable deaths from diseases like this–but this literally false way of putting it still undermines the appearance of credibility. When I’ve tried to persuade disbelieving friends that a vegan diet is healthy by suggesting they look at your posts, this is a criticism that often comes up.

    • bobluhrs

      My experience has been that people listen when the spear hits another. If it hits them, they tend to fall towards the one throwing it. In other words they take on more damaging load from drugs, surgeries, super-supplements, chicken soup, stand on their heads, bow three times to Chicago, etc. ineffective things or accelerants that won’t work and importantly won’t interfere with pleasure, since they are in pain. But if it hits someone else nearby or famous, like Bill Clinton, there’s a rustle in the survivor brain. I mention I’m on Clinton’s diet, seems to get favorable attention.

    • LaraineAK

      No you don’t have to die of diseases. Many elderly just have their ‘parts’ slow down and wear out. Sometimes the heart just stops…healthier people do often die peacefully–closing their eyes and passing. This has become much less common in our time.
      But even when diseases or disorder takes us, it should be very late in life.

  • Diane

    Doctor, what about metal detectors? For work (a PT job I don’t “need”), coming and going, I have to walk through a metal detecting machine and go through a full body scan with a wand. Are there negative consequences to that? Thanks,

  • philip litrel

    Monty you are on a thankless mission. You can
    only help people that want help or are open to improving their health. I have
    found that trying to persuade people, in general does not work. They must have a
    reason in their minds to give them a willingness to change or help themselves. This
    could be due to some health problems that they have, from obesity or diabetes
    to high blood pressure or vascular problems. Think about it, people that are in
    trouble (of any kind) seek help (pretty much from anybody) but people that (in
    their minds don’t have any problems) don’t seek help and usually resent advice,
    even it is helpful. Trust me I have been through this , help people that need
    it ( and know that they need it) they will be open and grateful. Good luck.
    Keep helping people it’s a good thing to do.

  • Jenny

    The statistics you presented are rather frightening. My daughter had a head CT for a fall when she was just 15mos. To think this may put her at significant risk of cancer is unsettling. Now that we know this risk what if anything can be done to reduce her risk?

    • bobluhrs

      I’m not sure, but it seems like once the exposure happens it’s too late to undo the changes. However, the plant-based diet is shown on this site to fight both the growth of new cancer cells, and to encourage the death of existing cancer cells. Thus the cancer could remain sub-clinical or even gone from the anti-cancer effects of diet, probably the sooner the better.

  • Leslie

    What about MRI’s of the brain? Any adverse consequences or damage as a result of having this procedure done?

    • VegAtHeart

      Unlike CAT scans which use x-rays, MRIs use lower energy radiowaves that will not produce damaging ions in the body. Nevertheless, MRI radiowaves have the potential to cause damage due to heating effects (for further reading look up Specific Absorption Rate (SAR)) or due to peripheral nerve stimulation; however, the specific MRI pulse sequences that are used in clinical practice have been designed with safety in mind and should not produce these adverse effects. The strong magnetic fields (1.5T to 7T, i.e. tens of thousand times stronger than the earth’s magnetic field) required by MRI to give good image quality, is not at present thought to be associated with any harm.

  • mitch

    I have been a CT tech for over 30 years and a lot of what has been posted is very true. No X-rays are good xrays. With that in mind it’s risk vs reward. If your child fell and hit his or her head and presents with symptoms of brain injury, of course, do the CT scan. If your child has a sinus condition with a head ache, then what do you do? In my experience doctors will do anything to cover their butt so they over use the CT scan to “rule out” anything so they don’t get sued..
    In the last few years the program of “scan gently” has greatly reduced the amount of scans ordered on children.

  • Avent Randall

    Do ECG tests present any danger?

    • mitch

      ECG’s and MRI’s don’t do any damage as we know it today.. ECG’s just read the electrical activity of the heart, like listening to the radio. MRI’s don’t use ionizing radiation like Xrays or CT scans (A CT is just a big computerized x-ray machine). So in a nut shell X-ray bad, all others not so bad.. MRI’s use a huge ass magnet and then pulse many thousands of watts of Radiofrequency through your body. If you have had a MRI, that’s the bang bang bang you hear.

      Just as an aside, I worked on one of the first MRI’s in the country. Our control/operator area was where the magnetic field was still prevelent. Pens and paper clips on the desk would align with the magnet. Every one of us had short term memory loss. We HAD to write down everything or we forgot it. Post-it notes all over the place!!
      Go on Vacation for a week and you were fine. Back to work= Forgetful. Thankfully there is more RF shielding in the MRI units today.

      • Avent Randall

        Thanks mitch. I just had an ECG and I’ve been avoiding x rays of all types.

  • Psych MD

    Welcome to the world of defensive medicine.

  • VegAtHeart

    I agree with the comment that doctors should ensure that their patients are thoroughly informed about the risks of ionizing radiation from CAT scans, though I have some doubt that there is widespread neglect by doctors in this area. I think most doctors do their best to inform patients, given the time constraints of their career and education level of their patients.

    Doctors who recommend CAT scans likely base their decision on a trade-off between the benefit of getting life-saving information from CAT scans versus the harms associated with them. For example, an oncologist who recommends a CAT scan for a patient showing indications of cancer will likely be gaining extremely relevant information that may save a person’s life. If it turns out that the CAT scan was non-informative, even though lifetime risk of cancer went up, the oncologist would not be to blame since they may have had no better way of making their diagnosis.

    I feel their is considerable edge in this article directed toward doctors, i.e. “doctors causing a lot of cancer.”. I think it is downright impossible for a typical patient who is a non-expert to decide what CAT scans are absolutely necessary when they don’t know what their symptoms are associated with…thus it is the role of the experienced doctor to help guide the patient on these topics.

  • Alef1

    I earned my Ph.D. in biochemistry looking at the effect of free radicals – also produced by radiation, and their involvement in the aging process. Aside from increasing cancer risk, high amounts of radiation greatly accelerates processes that simulate aging in many ways.

    So, just as a thought experiment I assumed that damage caused by background radiation accounts for somewhere between 1% and 10% of the aging process. After seeing the research of Dr. John Gofman, who convincingly demonstrated that even the smallest amount of radiation can cause harm, I chose the higher number of 10% as the one to use as a cautionary rule of thumb. I expect – hope! – that the actual contribution of background radiation with respect to aging seems much, much lower,

    So in this thought experiment, an X-Ray dose that gives a patient the equivalent of 10 days of background radiation, has aged the patient the equivalent of about 1 day – insignificant. But a lumbar spinal x-ray – equivalent to 158 days of background radiation, ups that to over two weeks of avoidable aging. And an abdominal CT scan – equivalent to 3.3 years of background radiation begins to get rather worrisome – 4 months of avoidable aging in an instant.

    Unfortunately, the effects seem cumulative. In our society, someone could easily get 10 to 100 times the abdominal CT scan dose from a series of visits to an x-ray trigger-happy doctor or hospital, just from diagnostic x-rays, resulting in 3.3 to 33 years! of avoidable premature aging. And getting years worth of radiation IN A FEW SECONDS from an x-ray machine, probably seems much more damaging than getting exposed slowly over over days, months, or years from natural background radiation, where the body has time to make repairs to minor damage before it becomes major.

    Furthermore these dosages assume X-rays machines in proper working order, and technicians who calibrate them correctly, and do not overdose.

    Finally, the dosages I refer to above compare x-ray exposures to whole body exposure from background radiation, but in fact some localized areas will get far higher relative dosages. An average brain weighs about 1 pound, about 1/150 of the mass of a 150 lb man. So if the brain gets selectively exposed to the same dose, say in a head CT that would cause the equivalent of 25 days of additional aging for a evenly distributed whole body exposure, this figure becomes greatly magnified for the brain when looking at a selective exposure to the head only, in what may amount to years of additional brain aging in a few short minutes. And hot spot areas might have even greater effects.

    So from my point of view, three things seem obvious from the Hippocratic oath’s “Do no harm . . . ” point of view.

    1. Only take x-rays – other than those that have a very low aging cost (like digital dental x-rays) – when necessary for diagnostic purposes, and when doing so, take the fewest x-rays at the lowest exposure levels.

    2. Effectively and routinely shield any areas of the body (especially the brain!) from unnecessary exposures – even from lower-dose x-rays – when taking diagnostic x-rays of other areas. At least make lead caps, blankets, etc. readily available for any patients that might want to make use of them.

    3. If at all possible provide the patient with known radioprotective supplements, or at least with a recommended list and protocol – like A, C, E , NAC, polyphenols like resveratrol, etc. or advise them to eat
    radioprotective foods, to take well before as well as after they receive any significant X-ray dosages, at least from CAT scans.

    4. Lower x-ray exposures from better machines obviously seem preferred to higher dosages given by older machines. I would gladly pay 10X the going rate or more to get an X-Ray from a newer model machine that provides the same information at a fraction of the radiation dose. For me, the monetary cost of an x-ray seems trivial when compared to the physiological costs in accelerated damage and aging as well as other, increased risks.

    My point of view.

    • Tommasina

      Wow, Alef1, thanks so much for sharing your research on here. What valuable information!

    • Nevo

      what do you consider to be “radioprotective foods”? Thank you.

      • Alef1

        Hi Nevo -
        As far as radioprotective foods go, check out “Radioprotective Potential of Plants and Herbs against the Effects of Ionizing Radiation” ( http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2127223/ ) for a review of many such foods.

        “The results obtained from in vitro and in vivo studies indicate that several botanicals such as Gingko biloba, Centella asiatica,Hippophae rhamnoides, Ocimum sanctum, Panax ginseng, Podophyllum hexandrum, Amaranthus paniculatus, Emblica officinalis, Phyllanthus amarus, Piper longum, Tinospora cordifoila, Mentha arvensis, Mentha piperita, Syzygium cumini, Zingiber officinale, Ageratum conyzoides, Aegle marmelos and Aphanamixis polystachya protect against radiation-induced lethality, lipid peroxidation and DNA damage.”

        Turmeric, just highlighted in some videos here, as expected has radioprotective effects:

        http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3453134/ , http://phcogcommn.org/2012/171

        I also like this overview article from LEF: http://www.lef.org/magazine/mag2010/aug2010_Protect-Your-DNA-from-CT-Scans-X-rays_01.htm that includes 111 references. Caveat emptor though – LEF sells supplements, and has a monetary interest in selling their supplements, and biases their papers to feature supplements, rather than foods. And while I’ve never caught them misquoting a paper, they select their quotes to support their point of view. They also routinely neglect to refer to research that contradicts their POV. I find their articles best used as a source for relevant references.

        I hope this helps!

      • Alef1

        See also:

        http://nutritionfacts.org/video/mediating-radiation-exposure-from-airline-travel/

        and http://www.gabrielcousens.com/DRCOUSENS/DRCOUSENSBLOG/tabid/364/PostID/151/language/en-US/A-Comprehensive-Holistic-Approach-to-the-Plague-of-Radiation-and-What-To-Do.aspx

        (Caveat emptor – many references not provided):

        “The fourth protection principle is that there are certain foods and herbs that specifically protect against the overall effects of radiation or radiation
        treatments. Foods containing chlorophyll have long been known to protect
        against radiation. Research has found that cabbage, leafy green vegetables, spirulina, chlorella, wheatgrass, any sprouts, and blue-green algae all reduce the effects of radiation. Additional foods that protect against radiation include:

        Soy miso according to post-Hiroshima research, was shown to increase resistance to radiation amongst laboratory mice by five times.

        Beets protect against the uptake of plutonium-238, -239, iron-55, and
        -59. J. Wolsieffer reported in the Journal of Dental Research, in 1973, that rats fed a diet of 20% beet pulp had 97-100% less cesium-137 absorption than rats exposed to the same radiation but not given the beet pulp. Beet juice is particularly high in a specific anthocyan, which is active against cancer and leukemia.

        Bee pollen is another potent antiradiation food. . . .

        Garlic, onions, and ginseng are also protective against radiation due to
        antioxidants and factor X.
        . . .
        Siberian ginseng is an outstanding protective herb as an adaptogenic to double post-radiation lifespan of rats. . . .

        Chaparral contains a potent anti-oxidant known as NGRA. It was one of the
        few plants to survive atomic testing in Nevada.

        Herbs including astragalus, echinacea, panax ginseng have all been shown to
        counteract radiation toxicity to some extent.

        . . .

        After 55 years of being listed as classified, research has released showing
        that 20 cups of green tea a day gave 97% or more protection against exposure to
        the atomic bombs over Hiroshima and Nagasaki. For this reason alone green tea should be in the number one category for protection against radiation
        exposure.

    • Merio

      I think i would ask you more information about this topic… gimme the time to earn my degree in Biotechnology… even if i studied this topic (not deeply) my professors do not talk about this issue…

  • Richard

    Thanks so much for your information.Thinking about the technique of detection of breast cancer (mammography) in which the procedure is very uncomfortable for women and because there is no new technical about it, what is your opinion?

    • Thea

      Richard: You may be interested in this:

      “”McDougall Breaking News – The Cochrane Committee now recommends against mammograms for women of all ages. Screening for Breast Cancer with Mammography – Published by the Nordic Cochrane Center 2012. What are the benefits and harms? How many will benefit and how many will be harmed? What is the scientific evidence?” – Source Dr. John McDougall
      http://www.drmcdougall.com/misc/2012other/news/jun/mammogram.htm

      I found the above document to be extremely compelling and helpful.

      Hope that helps you.

      • http://www.DonForresterMD.com/ Don Forrester MD

        For those interested in the details behind the recommendations in the pamphlet by the Nordic Cochrane Center Peter Gotzsche’s book on Mammography Screening: Truths, Lies and Consequences is thorough. As a Family Medicine physician given the current science it is difficult to recommend mammograms as screening. This doesn’t apply to the use of mammography as a diagnostic test for masses and certain abnormalities. I find the pamphlet to be well written and should be read by any women who is considering screening mammography.

        • Thea

          Dr. Forrester: Thanks for this additional information! I hadn’t known that there was a book behind the pamphlet I referenced above. In looking for the book you mention, I came across Dr. McDougall’s full article on this topic and that was another great find. Thanks!!

          For anyone interested:
          http://www.drmcdougall.com/misc/2012nl/may/mammography.htm

  • Edward Medrano

    Hello Doc I am extremely frightened by this news, I have had 4 or 5 CT Scans in the abdominal area since I was 16 or so. Now I am 19 years old and I am extremely worried of my own well being. I read in another post that the CT scans were only a small percent of getting Cancer. But with all this news I keep hearing a cannot bare to hear this anymore. I feel depressed and hopeless at times. What can I do. Im a type of person who is very paranoid when it comes to this issue.. Any advice????

    • Thea

      Edward: I am not a doctor, but I hope I have some thoughts that may bring you some peace.

      I think the CT Scan information concerning cancer is just like “gene” information concerning cancer. For example, just because a person has the “breast cancer gene”, does not mean that the person will actually get breast cancer. While I would guess that you are now in a higher risk bracket, you are not destined to get cancer.

      While there are some things you can do nothing about, such as past CT Scans, there are plenty of things you can control which affect whether or not any bad cells in your body reproduce enough to give you any troubles. I highly recommend that you spend some time looking at the (many) videos on this site which discuss how diet affects cancer. You can figure out which foods to avoid and which to focus on. While such a step is not a guarantee, adopting a healthy diet will give you a lot of control over your health and go a long way to reducing your risk of actually developing cancer. Just to get you started, here are Dr. Greger’s nutritional recommendations, though you will want to research the cancer videos specifically to tweak the diet for your concerns:

      http://nutritionfacts.org/2011/09/12/dr-gregers-2011-optimum-nutrition-recommendations/

      http://nutritionfacts.org/index.php?s=cancer

      In addition to diet, you might consider doing some research on other factors you can control. For example, I understand that a lot of cleaning other household products are toxic. So, maybe you could look into cleaning up your living environment.

      Etc. I wouldn’t get yourself overwhelmed with changes. Maybe focus on diet today and when you are good, start to focus on other things. It certainly can’t hurt and maybe it will help alleviate not only your risk, but your concern and fear.

      Best of luck to you. I hope this helps.

      • Edward Medrano

        How long does it take for the damage to take effect. I read in a post it usually occurs later in life, the estimation was about 15-20 yrs. Is this any true for my own sake?? Thank You

        • Thea

          Edward: I’m not a doctor and have no way of knowing. But this is where understanding how cancer growth rates are so important to this question and how you may be able to slow the growth so that it is a problem for maybe 80 years. Who knows, but the science seems to back up the possibility of having such an effect.

          I highly recommend that you check out the videos on this site around cancer. Here is a video concerning growth rates.

          http://nutritionfacts.org/video/slowing-the-growth-of-cancer-3/

          I think this is a very encouraging and empowering bit of information. If you started now, there is the potential to have a big effect.

          Hope that helps.

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