CT Scan doses vary wildly depending on the type of X-ray (chest, head, limb, etc.), the size of the person, and a lot of other things. The bigger the cross-section of the thing you put in a scanner, the greater the exposure. CT machines themselves also vary considerably. Newer machines are often more sensitive and employ better imaging software, so they can do their job while delivering a much smaller dose. Anyone who quotes a solid number is probably using one that's absolute worst-case, which probably means a chest scan on a fat dude with a CT machine that's been around as long as disco music.
Personally, I like to think of medical imaging in terms of how long I'd have to work as a flight-attendant to get the same dose. When you fly at high altitudes (as most passenger jets do) there is less atmosphere to block cosmic radiation, which is the source of background radiation that we're exposed to every day. You get a higher dose of radiation at high altitudes amounting to a few tens of microsievert's for a decently long flight. Medical X-Rays that consist of a single photo are approximately in the same ball-park as an intercontinental flight or two, or working as a flight-attendant for a day or so. CT scans are in the ballpark of several months working as a flight-attendant. It sounds bad at first, but flight-attendants aren't known to have a massively increased rate of cancer after doing the job for decades.
In general, people fear radiation to an extent that is out of proportion with reality. To add more perspective, the background radiation in your living room will add up to a CT scan, most likely, in less than a year (unless you live in very deep mine). You can marginally improve your odds of getting cancer by avoiding medical scans, but only at the cost of massively increasing your odds of dying from something those scans might have helped diagnose. It's not an intelligent trade-off. Yes, unnecessary CT scans are bad, but not as bad as the article claims. The greatest cost of an unnecessary CT scan is probably to those who don't get scanned due to high demand on the machine. This article, by stoking irrational fears of medical imaging, is more likely to harm people than help them.
Note: Medical imaging is generally not done very often, is tracked, and is usually performed by trained technicians with quality apparatus. The same is not true of security X-Ray scans, which people can be subjected to much more frequently, are frequently performed by the near-unemployable, and use machines that are not designed with the primary goal of helping those it scans. The U.S. is also starting to use truck-based scanners to scan parked vehicles and people on public streets. You may be scanned by these not only without consent, but without knowledge. I do find this to be objectionable.
A lot of CT scans are well under 2 mSv. A lot more than you would expect from reading the worst-case estimates, as I mentioned above.
The increase in cancer rates is interesting though, although if the main cause was radiation you wouldn't expect a few specific types to increase significantly and not others.
"although if the main cause was radiation you wouldn't expect a few specific types to increase significantly and not others."
How do you figure? I don't think all of the causes of cancers are well understood. But, I know that cervical cancer is highly correlated with HPV, skin cancer is highly correlated with sun exposure, stomach cancer is highly correlated with H. Pylori, and lung cancer is highly correlated with tobacco smoking. And, for that matter, that cancers seem to have wildly different occurrence rates to begin with.
It's not even necessary to posit a 'radiation-associated cancer' category to account for differential cancer increases, as long as there are some cancers somewhere that pop up in response to things other than radiation. Existence proof: Cervical cancer, associated with a virus. We would not expect cervical cancer rates to jump to the same degree as $generic-cancer, because the radiation-caused rate of cervical cancer is only a small chunk of all cervical cancers: double it and you affect the overall rate little.
With that said, airplanes are doused in some other questionable chemicals as well - I've seen concerns expressed specifically about the breakdown of fire retardants.
This doesn't quite work. Suppose all cancers can arise in response to radiation, or for other reasons. Then an increased dose of radiation can boost them all equally (doesn't have to, but can). And the existence of non-radiation causes for cancer is completely irrelevant.
To argue that cervical cancers should jump by a smaller amount than other cancers in response to radiation, showing that cervical cancers are largely caused by something other than radiation is useless -- you need to show that other cancers are largely caused by radiation.
While your comment as a whole is thoughtful and well written, I'm surprised to hear you say, "Medical imaging is not done very often..."
Medical imaging is commonly overused, and its overuse is recognized as being one of the leading causes of certain types of cancer. For example, the original story explains...
"In a 2011 report sponsored by Susan G. Komen, the Institute of Medicine concluded that radiation from medical imaging, and hormone therapy, the use of which has substantially declined in the last decade, were the leading environmental causes of breast cancer, and advised that women reduce their exposure to unnecessary CT scans." (The substantial decline refers to hormonal therapy, not imaging.)
That is a great, powerful, article. Thank you for posting the link.
> For an individual woman in her 50s, then, annual mammograms may catch breast cancer, but they reduce the risk of dying of the disease over the next 10 years by only .07 percentage points — from .53 percent to .46 percent. Reductions for women in their 40s are even smaller, from .35 percent to .3 percent.
Many people are going to be baffled by risk presented like this. Presenting the numbers differently is helpful to let people understand the risks.
"Imagine 10,000 women like you. Of those X will die from this disease. But if we take those same 10,000 women and give them mammograms we find that Y will die from the disease".
Sometimes X will be 2 and Y will be 1 (50% decrease in risk) or X will be 100 and Y will be 2 or X will be 100 and Y will be 99.
Presenting the numbers this way allows most people to understand the risks better.
MRI is very different from CT. CT use X-rays, which is an ionizing radiation. MRI uses a very strong magnetic field, and as far as we know it doesn’t increase the cancer rates.
The final images are quite similar in appearance (semi transparent films with a black background), but the underlying process is very different.
I've lived in both the us and Canada. I noticed that mri and CT scan scans were really easy to get done in the us, but would often require a month or more of waiting in Canada for non Urgent issues. I wonder how much the overuse contributes to differences in health care costs between countries?
As someone now in Hong Kong about to fly back home to SF, I have always tried to schedule my flights so that I minimize my exposure to day time radiation. I guess I'm in the minority, but it's something to consider when taking international flights.
Then, in 1912, Victor Hess carried three enhanced-accuracy Wulf electrometers[12] to an altitude of 5300 meters in a free balloon flight. He found the ionization rate increased approximately fourfold over the rate at ground level.[12] Hess also ruled out the Sun as the radiation's source by making a balloon ascent during a near-total eclipse. With the moon blocking much of the Sun's visible radiation, Hess still measured rising radiation at rising altitudes.[12] He concluded "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." In 1913–1914, Werner Kolhörster confirmed Victor Hess' earlier results by measuring the increased ionization rate at an altitude of 9 km.
Some claim that wifi and cell phone emissions bouncing around in the cabin are also cause for concern. I've no idea if it's true, but I can imagine that inside an aluminum tube 150 wifi cards trying to connect might have some biological effect.
Absolutely -- you can get RF burns from holding antennas, and you can obviously see the results of massive radars (e.g. putting a gerbil in a microwave).
What we're arguing about is the signal strength and duration (and to some extent, where on the person the radiation is administered; hands are pretty tolerant compared to brain or torso), and the conversion factor to biological effect (which varies by frequency).
With modern radios, you've also got duty cycle -- your cellphone isn't transmitting full-time.
I'm basically not afraid at all about "tower" signals as a member of the public. I wouldn't stand in a microwave point to point beam. I also wouldn't want a 5W HT radio next to my head (or groin) for high duty cycle use, but I'm ok with holding it in my hand with a hands-free kit.
The people who vote you down for saying some types of non-ionizing radiation can be bad are actually worse scientists than if you were to say all (non-ionizing or ionizing) radiation is a huge problem. We have positive evidence that some radiation is really bad, and some is sort of bad; we have a bunch of negative confirmations that low levels of many kinds of radiation aren't likely to be very bad, and certainly aren't super-bad, but the exact borderline isn't known, and varies, and a 0.01% increase in cancer with zero benefit is more of a concern to me than a 1% increase in cancer with massive benefit (e.g. a CT for trauma where you'd otherwise be likely to die).
(Incidentally, my fear of ~200 wifi devices transmitting in the milliwatts on 2.4GHz or 5.8GHz or on a flight is approximately zero -- especially since it's unclear how many would actually be using the service at any given time, and it's a pretty large volume.)
I don't know why this was down voted; while in an elevator one is not supposed to use a cell phone, because of this effect. At least in the elevator at work there is a sign that says so.
I thought one is not supposed to use a cell phone in the elevator because it doesn't work because elevators are made out of ferrous metals and hence are effectively Faraday cages.
That "in the elevator at work there is a sign that says so" is hardly evidence for anything.
People use cellphones in elevators ALL the time, ALL around the world. Especially when continuing a conversation they had as they walked in the building, and for as long as the signal stays.
The evidence was in the link of my post: because of the Faraday cage/screening, part of the radio waves that the cellphone is emitting are reflected back into the elevator; the resulting strength of this fields exceeds the norms by an order of magnitude. this is considered to be within harmful range.
The parent poster mentions the same effect in the context of aeroplanes.
The elevator/order-of-magnitude thing is an urban legend.
You'll only find it mentioned in fringe non-scientific sites.
Case in point, your source, microwavenews. This is for the kind of people who believe in chemtrails and such.
I mean, even if you don't know about the site, isn't it obvious from the BS way of writing that you're reading something designed to sell stuff to kooks? "According to some new calculations", "if you believe the research by", obscure "EMF" conferences in China (with dead webpages) and what have you.
I don't know much about medicine and radiation, but is intensity a factor? Could getting x amount of radiation in 60 seconds be a bigger danger than the same amount of radiation spread out over days or months?
Yes, it can, and often is. Consider Albert Stevens. [1] He was (without his knowledge or consent) injected with a dose of 131 kBq of Pu, yielding a lifetime exposure of around 64 Sv. (An acute dose of >= 5 Sv is usually fatal.)
I'm not a doctor, but the way I understand it cumulative exposure is what really matters.
Ionizing radiation, such as X-Rays, tends to pass through matter with less interaction than lower energy EMR, such as light. Obviously, there is some interaction or it wouldn't be good for imaging! When ionizing radiation is absorbed it (as the name suggests) ionizes an atom by knocking an electron free. That ion will then probably form a bond almost immediately, altering the molecule it's a part of. If that molecule is a cell-wall, piece of enamel on your teeth, etc. the change will be harmless. There's a small chance it could be change to the DNA of one of your cells though. Most changes are probably harmless, but some can cause the cell to replicate out of control. i.e. Cancer.
Basically, getting cancer is like winning the lottery, and radiation gives you tickets. It doesn't matter if you get them all at once or spread them out. You might think radiation sickness is evidence that acute exposure behaves differently, but it actually takes several centuries worth of background radiation exposure to induce mild radiation sickness, so you're already operating in a whole new ballpark.
Your body repairs tissue tears and damaged cells as well as fighting off infections and things but I don't believe it is well-equipped to deal with damaged genes. I could be totally wrong, though.
DNA repair is happening all the time -- this is a major benefit of having double-stranded DNA.
Wikipedia offers DNA damage rates of 1e3 - 1e6 DNA damage events per cell, per day ( http://en.wikipedia.org/wiki/DNA_repair ). Almost all of these get repaired.
Generally, the unit in which exposure to ionizing radiation is being measured is "Gray" (Gy) which is absorbed energy (Measured in Joules, equal to one Watt-Second) per kg of absorbing material. That's called the "Dose". If you account for the amount of damage that this Dose can do to humans, you'll call this weighted Dose "Sievert" (Sv). Generally the weighting is not that important for X-Rays or gamma-radiation (the "normal radioactivity" people are concerned about), but will be important when dealing with neutrons.
If a person is subjected to 5-10 Sv instantaneously, so many cells will be damaged that this person will die, not of cancer but of multiple organs ceasing to function properly over the course of a few days.
But, as you already have written, that's about 2000 years of background radiation (3mSv/year) in a very short time (documented accidents: probably few or less than one second). -> http://en.wikipedia.org/wiki/Background_radiation
There's data from survivors of the Hiroshima and Nagasaki bombs, and this data corresponds to exposure to about 50mSv to 2Sv. There are also other studies, including people living in areas with hither (or lower) natural radiation levels, working in former Soviet-Union closed-off nuclera-research areas, and so on... (http://www.nap.edu/openbook.php?record_id=11340) All these "cohorts" (as they are called: a number of test subjects) have been studied for health effects. And a lot of people that got high doses died of cancer. Unfortunately everyone of us has a high high probability of getting cancer at some point in his life. And it turns out that you need a lot of radiation to double the risk of getting this disease:
The straight line in this plot represents the "linear model" which assumes that the additional chance of getting malignant tumors rises just the same as the amount of radioactivity. But then, if you go down to the very-low-end, which is very, very, very difficult to analyze, because you are looking at only miniscule differences in cancer-rates, sometimes people find that it appears that a small amount of radiation might even be beneficial and reduce the risk of acquiring cancer in a lifetime.
We get cancer all the time, our body kills it. So rate plays an important part. If a CT scan is months worth of exposure, the time for our body to react to new mutations is drastically reduced.
This is a good example of how hn is suffering from the real slashdot effect lately. That is, people posting authoritative sounding but completely wrong information and getting upvoted for it.
Personally, I like to think of medical imaging in terms of how long I'd have to work as a flight-attendant to get the same dose. When you fly at high altitudes (as most passenger jets do) there is less atmosphere to block cosmic radiation, which is the source of background radiation that we're exposed to every day. You get a higher dose of radiation at high altitudes amounting to a few tens of microsievert's for a decently long flight. Medical X-Rays that consist of a single photo are approximately in the same ball-park as an intercontinental flight or two, or working as a flight-attendant for a day or so. CT scans are in the ballpark of several months working as a flight-attendant. It sounds bad at first, but flight-attendants aren't known to have a massively increased rate of cancer after doing the job for decades.
In general, people fear radiation to an extent that is out of proportion with reality. To add more perspective, the background radiation in your living room will add up to a CT scan, most likely, in less than a year (unless you live in very deep mine). You can marginally improve your odds of getting cancer by avoiding medical scans, but only at the cost of massively increasing your odds of dying from something those scans might have helped diagnose. It's not an intelligent trade-off. Yes, unnecessary CT scans are bad, but not as bad as the article claims. The greatest cost of an unnecessary CT scan is probably to those who don't get scanned due to high demand on the machine. This article, by stoking irrational fears of medical imaging, is more likely to harm people than help them.
Note: Medical imaging is generally not done very often, is tracked, and is usually performed by trained technicians with quality apparatus. The same is not true of security X-Ray scans, which people can be subjected to much more frequently, are frequently performed by the near-unemployable, and use machines that are not designed with the primary goal of helping those it scans. The U.S. is also starting to use truck-based scanners to scan parked vehicles and people on public streets. You may be scanned by these not only without consent, but without knowledge. I do find this to be objectionable.