Thinking about risk

March 21, 2009  |  General

I’ve recently been looking over the statistics about this blog. The most popular posts are those which talk about common issues — croup and concussions, for example. But one of the most often read posts gets its popularity from people using search engines like Google to answer this question: how risky are x-rays, especially CT scans, to children? You can read my actual posts about that here and here, but what struck me most about the popularity of this topic is what it tells us regarding how we think about risk. In particular, how do we tend to think about the risk of events occurring which are very rare, but which carry grave consequences if they happen? Lawyers call these events “small probability — large loss events.” Economists have studied the subject quite a bit, too, especially as it relates to investment decisions people make.

We humans are not entirely rational when we think about risk. We tend to focus on low-probability but high seriousness events, particularly if we are thinking about them in the context of choosing to do or not do something. So, for example, if your child needs a CT scan, as a parent you many think about how the radiation in that test increases your child’s chances of getting cancer. What we don’t think about is that your child is far, far more likely to suffer harm in a car accident while you are driving to the CT scanner than he is to suffer harm from the scan. But since we drive our children around every day, we don’t think much about that risk.

According to the National Cancer Institute, a child’s overall risk of developing any form of cancer is 1-2/10,000 children, or 0.01-0.02%. Also according to the NCI, this number has changed very little, if at all, over the past 30 years. The use of diagnostic x-rays in children, especially CT scans, has increased enormously during that time, so we should be reassured by these statistics. Even so, radiologists are increasingly vigilant about how they can reduce radiation exposure when they use x-rays.

Bottom line — it is always worth asking if the risk of a test exceeds the value of the information the test will give. But for x-rays, the benefit virtually always outweighs the risk.



  1. Dear Dr. Christopher,
    It happened three days ago, on 16-10-11.
    My grand daughter, 7 months old, fell down from the sofa, to the floor, which had a cushion. It was a fall head down. The child cried for some time and became normal. I felt bad because the child was under my care.
    Her father was not at home. I had to take a decision.
    It was 7 pm. I had to rule out the possibility for any complication.
    I took her to the emergency ward of the nearest public hopsital. The doctor said there was no visible complication and advised a head x ray. I asked what
    was the risk invovled. He did not give an answer and said head xray was needed.
    The Radiologist who did the xray appeared to be totally unprofessional. He was messy. He had no to handle a baby. He did not cover the areas not to be x rayed.
    He took two photos, one staight on the face, other from the side view.I do not know the ratiation level used.

    I am terribly upset. Have I caused life long problem for rhe baby.
    Can you tell be what are the possible complications and what are the precautions possible?

  2. I wouldn’t worry about 2 simple skull x-rays. Really, there should be no life-long complications from this — the radiation received is about the equivalent of the normal background radiation of about a month of normal living at sea level or of a long airplane flight.

  3. Hi,

    I just want to say thank you for your helpful, knowledgeable posts. My 5-month-old son has a very large head (47.7cm) and my pediatrician has been vigilant about frequent measurements. He had a skull x-ray at 3.5 months to make sure there was no premature fusion. After the 47.7cm measurement yesterday my doc sent him for a CT (without contrast). He told me he was concerned about Arnold-Chiari malformation or, again, suture fusion. My husband and I were pretty sure there was nothing wrong – no symptoms, and also he is a big boy overall (21.5 lbs and 28 inches); and my husband’s noggin is so large he has to special order hats and helmets. But we went for the CT at a pediatric radiology place, got a stat read, and of course everything was fine. I then drove myself crazy last night becoming more and more upset about the unnecessary radiation we had exposed him to. My doc told me when I sort of balked at the CT yesterday that “98 out of 99 pediatricians would order a scan seeing this head circ graph,” but I feel like as a mother I should have protected my baby when I really believed nothing was wrong. Also we are supposed to be flying with the baby in a couple weeks, do you think we should cancel to prevent additional radiation exposure at this tender young age? Thank you so much for your website.

  4. Hi Leslie:

    As you know, these are tough questions. The big one is always weighing the risk from the radiation (which, although not zero, is still very, very small) against the risk of not having the information the scan gives. Of course I can’t speak about the details of your doctor’s decision-making because I’m not your child’s doctor. But if the doctor was concerned about the possibility of Arnold-Chiari or some other condition then I would lean toward doing the CT because the information would be important in your child’s care. So I’m not sure at all that radiation was unnecessary. It’s all a matter of relative risk. You know now that the CT was normal, which makes you wonder if you should have refused the scan, but there was a real possibility that it would not be. And the lack of any symptoms, although encouraging, doesn’t mean the scan could not be abnormal.

    I wouldn’t worry about the plane flight — the radiation exposure is tiny. There is some information regarding flying and cancer risk: airline pilots, even after 40 years of flying, have no higher risk of cancer. I realize those are adults, but you should be reassured by that research.

    I can’t tell you not to worry, because all of us worry about our children — that’s what being a parent means. But it sounds to me like you did the right thing.

  5. Thank you!

  6. Hello, and thank you for this website, it is very informative.
    I have some concerns regarding my daughter’sexposure to radiation at a very young age. Firstly, I had to undergo a brain CT when I was 32 weeks pregnant. Then, as a newborn they x-rayed her chest -2 views, and at 3 months she had several skull x-rays, I think 5 or so.
    I now live in fear that this radiation will cause her to have cancer in the future. I realize that I cannot undue what has been done, but can you please give me some insight as to how significant this exposure will be for her? Thank you.

  7. Hi Trudy:

    I wouldn’t worry about that degree of radiation exposure. The chest and skull x-rays have very small amounts of radiation. The CT had a higher dose, but you received that, not her.

  8. My son, 10 weeks old, has been having feeding issues since birth. He always cries with his feedings. The past few weeks he has only taken in half ounce to 2.5 ounce on a good feed. He is breasted and I know the ounces as I have been giving him pumped milk every so often. By breast he stays on for 5 min before he cries. The pediatrician order a milk scan and upper gi on him. The test came back normal so I fell very guilty for putting him through this radiation At 2 months old. I have been so worried about his chances of getting cancer. Should I be this extremely worried?

  9. Hi Emily:

    I wouldn’t worry about that amount of radiation at all. But your comment illustrates what I’ve been writing — always balance the risk of doing the test against the risk of not having the information the test gives. You say you feel guilty because the test came back negative. But you didn’t know before the test which way it would go, and the radiation risk (which is inconsequential) is the same either way, if it had been positive or negative. What I mean is that the way to think of it is that your doctor needed the information, and negative information is often just as helpful as a test that shows an abnormality.

  10. Hi Christopher what do you think of this study.
    My son had to have 2 x rays as a result he may have ingested a button battery.thanks

  11. I don’t see a link to a study in your comment. But in general eating button batteries is potentially quite serious so a variety of studies are often needed to deal with the problem. At any rate, 2 x-rays should be no big deal risk-wise.

  12. Hi there,
    I was quite a sickly kid growing up and had several X-rays on chests, sinus, hips, spine and a head CT when I was 13. I am now 30 and I have been through the diagnostic imaging gauntlet again the past 10 years as follows:

    Age 13 – CT for sinus
    Age 4 sinus xray
    Age 2 xray of hips
    3-4 Chest X-rays ages 3-18
    Abd xray age 7
    At least 3 S&D’s w/follow through age 20′s
    At least 3 BA Enemas age 20′s
    SPINE xray x2 age 20s
    Chest xray age 29
    Bilateral mammo age 30
    Abd pelvic xray age 30 nov2014
    Ct sinus dec 2014 age 30

    I don’t know how to calculate risks – I’m just terrified now that I have destroyed my body even though I was just following doctors orders. They have never discovered any serious pathology with these tests. So I’m wondering I’m the grand scheme of things if my overall cancer risk has sky rocketed from these procedures that I went through because I didn’t educate myself on the riskiness of all this radiation.

    Hoping to get some perspective as I am very anxious about this.

    Thank you for your time!!

  13. Hi:

    Overall your risk isn’t increased much by those studies. Really — try not to worry about it, hard though that may be. Your cancer risk certainly hasn’t skyrocketed with them. Maybe a hundredth of one percent at most.

  14. Thank you so much for your time!

    I really appreciate your perspective. I keep getting differing opinions from technicians, doctors, family and of course from “dr. Google”. It’s nice to hear from you, even though I’m not your target patient age.

    Take care,

  15. Dear Mr Johnson,

    The reason I am contacting you is because in the country where I come from (Bulgaria) the health practitioners do not seem to be very concerned about the long-term consequences of x-ray on infants. However, the parents are those who remain worried about eventual ALL or other cancer. The long story short – when my baby boy was 2 weeks old he got two barrow swallow x-ray fluoroscopies. The doctors suspected pyloric stenosis. After they did the first fluoroscopy, the diagnosis was rejected but we remained hospitalized. Five days later the baby started vomiting again and the doctors doubted their initial conclusion and ordered another fluoroscopy. The second fluoroscopy was performed and it had a follow up procedure in 3 hours (I still do not know whether the follow up procedure was just a single image or something severe as fluoroscopy). The final conclusion was reflux, rather than pyloric stenosis and we were sent back home. In addition, my baby had a single image x-ray on the head (not a head CT) as he fell badly when he was at the age of 1.
    I keep blaming myself that I let the doctors to perform the fluoroscopy twice to a newborn. I tried to obtain information from the hospital about the radiation to which my child was exposed, but unfortunately they first started to collected such data some months after the x-ray exams were performed to my son.
    I have been reading a number of articles on the risks associated with x-ray, especially in childhood. I realize that there are many negative factors accumulating in our case – the age (only two weeks old), the type of the exam (very severe radiation expose in comparison to a single x-ray), the number of the exams and follow up exam. I am trying to estimate somehow the risk and I can not. Most articles refer to head CT scans and I read that the barrow swallow x-ray fluoroscopy actually carries greater exposure to radiation in comparison to a head CT scan.

    Needless to say, me and my husband are extremely worried about the risks and shall appreciate very much your opinion.

    Best Regards,


  16. Hi Svetlana:

    I have a couple of thoughts about your experience. The radiation dose from fluoroscopy is not precise because different radiologists use slightly different doses. This is because the fluoroscope is turned on and off (usually with a foot switch) by the radiologist during the procedure as he or she watches the barium move through. Even so, a good estimate of the radiation dose of an upper GI study or barium swallow in the hands of a skilled radiologist is actually close to that from a head CT scan (about 6 mSv). This is less than for an abdominal or chest CT, which are closer to 10 mSv. So I think your child’s total dose is roughly similar to 2 head CT scans. The follow-up study after the barium swallow was probably what we call a small bowel follow-through and was probably just a single image of the abdomen. That one and the skull x-rays when he fell have tiny radiation doses, so I wouldn’t worry about them.

    In terms of lifetime cancer risk, the 2 fluoroscopy procedures probably raised your child’s cancer risk by 0.1% at most. But you need to put that in perspective. At least in the USA, the lifetime cancer risk for a male is around 45% already. So the small increase in cancer risk at worst would make your son’s risk about 45.1%. That is real, but still quite small effect overall.

    I share your concern that doctors should consider radiation risk more than they do. But the key thing is weighing the risk of the x-ray against the risk of not having the information that the x-ray gives. The real key is not to do a fluoroscopy or other study unless you really need the information to make a decision about the best thing to do for the patient. So in the future a good thing to do is ask the doctor: What are you going to do with the information? How necessary is it to have the information to decide what to do? What is the risk of NOT having the information? These are thing things that allow us to decide what we call the risk benefit ratio: the risk of doing something vs the risk of not doing something. Of course that applies to any medical test or procedure.

    I hope this helps you.

  17. Dear Mr Johnson,

    Thank you for your time. Me and my husband really appreciate your opinion.

    I now realize that the risk is really small. In one of your articles you describe this as “small probability – large loss events”. Being a practicing lawyer, I have an idea what this phrase accounts for.

    Thank you again for your time and effort.

    Best Regards,


  18. Dear Mr. Johnson,

    My 8 year old son complained about his shins hurting and we went to see a specialist. She ordered some x rays of the hip and thigh bones. Not aware of the radiation risk factors of x rays at the time, I suggested to the doctor to take x rays of his shins a well since his pain was primarily in his shins. They took 1 of his hips, and 17 others of his knees, thighs and shins. It turns out that he has shin splints. I came home after the fact and started googling….. and am sleepless from everything I’ve read about the dangers in too much radiation. I went back to the hospital and spoke to a radiologist there and they told me that they had used a lower dosage suitable for children and that I have nothing to worry about. A lead apron was used. They took 18 x rays in all. I am so worried that I might have put my child in greater danger.


  19. Dear Mr. Johnson,

    My 8 year old son was complaining about shin pain. We went to see a specialist who ordered 18 x rays – 1 pelvic, 17 of the legs, knee and shin. Is my son in danger of great risk?


  20. Hi Helen:

    Actually that number of what we call plain films is not a substantial amount of radiation. So, as the radiologist said, I wouldn’t worry about it if it were my child. It’s the CT scans and fluoroscopy that have the large radiation doses, not the plain films.

    Hope this helps you

  21. Hi, I’m worried about my little boy. He had an xray aged 1week old to check his heart as he had a few blue episodes. They all came back clear and he is now 14months old. However he has recently been getting poorly a lot and having petechiae and swollen glands so I’m terrified of leukemia. The docs have done a full blood test and I think most of it was ok but have been told to call the docs to discuss results but that out isn’t urgent. I can’t stop worrying that I’ve damaged him

  22. Hi, I’m really worried I might have damaged my little boy. He had an xray at 1week old to check his heart as he had had a few blue episodes. I don’t think they covered the rest of him at all so he got zapped (I wasn’t there as it was the middle of the night in hospital and he went with my husband coz I was too upset) xray came back fine but I’m now worried ours harmed him. He’s 14months old now and had recently been quite poorly-onev thing after another and swollen glands /petechiae spots. GP ordered full blood count test and got told on Fri that he wants to talk to us but that it isnt urgent. I’m absolutely terrified I’ve caused him to be ill or something

  23. Sorry for accidently messaging twice!

  24. Hi Sarah;

    Don’t worry at all about a single x-ray like that. It carries essentially no risk for his health. It has more or less the same radiation dose as he gets naturally during 10 days of life at sea level (more like 7 days of normal life where I live — 7,200 feet). It also has about the same radiation dose as a 4 hour long airplane flight, during which the airplane spends about 3 hours at 37,000-39,000 feet of elevation. The radiation we get in that way is the background radiation from outer space. It’s all around you, but stronger as you get closer to outer space.

    So really, don’t worry about the x-ray. The doctors needed it at the time to look at his heart. But do follow up with your doctor to see what your boy’s blood counts are. If they are abnormal he might need other tests.

    I hope this helps you

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