Impossible to draw any conclusions from such a convoluted and problematic model. No mention of how they determined patients were unique, or whether multiple scans were counted for a single patient. No mention of patient data - seems that covariates were estimated, leading to greater uncertainty. For example, we have no idea if any of these patients already had cancer before getting a scan. And of course, this entire model is incapable of answering the question that patients actually care about: not "will I get cancer from this?" but "will this scan more likely increase or decrease my lifespan and/or quality of life?".
Seems pretty common sense to me that you're gonna have more people with hidden cancers coming in to get CT for phantom pains, etc and later discover they had cancer all along. That doesn't mean CT caused it. Did the study control for this?
No, because that's not how the study worked, i.e. it wasn't actually tallying cancer rates from people who had CTs. It basically just looked at the amount of radiation that a CT scan gives a person, and then extrapolated the cancer that would be expected from that radiation dose based on other data we have of e.g. people exposed to radiation in their jobs, and nuclear fallout occurrences.
Previous studies I've read did account for this, and put the number at about 3%. That said CT manufacturers have been working on a bunch of technology to make this better, either by doing a better job at not aiming at sensitive areas or by reducing the amount of radiation needed to get the same resolution in the images.
The whole dataset seems like something hard to work with, population that needs CT scan in the first place is very biased, people don't do CT scans for fun but because there is something weird that docs can't explain already.
It's unclear to me whether you read the journal article or just the Ars article? If you're referring to the journal article that gives your assessment much more weight.
I went to the doctor complaining of constipation. He sent me for a CT scan which showed that I was literally full of shit. The prescription was for a large dose of MiraLax. Now I wonder if the risk of the CT scan was really justified given that plenty of people already tell me that for free and without radiation.
A. Newer CT scan machines use lower radiation doses.
B. If you're getting only one scan a year you're fine and within yearly limits of radiation dosage considered acceptable.
Remember that you'll get comparable levels of radiation even if you commute through the grand central station every day.
This paper is for lack of a better word, crap. It's becoming sensational for the conclusion it makes and I'm afraid it's now going to create more harm because of that.
> Remember that you'll get comparable levels of radiation even if you commute through the grand central station every day.
Gemini says this:
> A single typical CT scan delivers a dose that is roughly 1,000 to over 5,000 times higher than the dose you'd get from spending a few hours in Grand Central Terminal.
Was it hallucinating here, or are the commenters hallucinating? What OP is saying is just not true. A CT scan and normal daily commute in Grand Central station are NOT comparable in terms of radiation received. Somehow this is controversial because an AI said it?
The machine appears to have hallucinated the incomparable comparison, instead of a human.
(And I'm not picking on the machine at all here. I use it all the time. At first, I used to treat it like an idiot intern that shouldn't have been hired at all: Creative and full of spirit, but untrustworthy and all ideas need to be filtered. But lately, it's more like an decent apprentice who has a hangover and isn't thinking straight today. The machine has been getting better as time presses on, but it still goes rather aloof from time to time.)
What do you mean all LLM output is hallucination? Would you say the same about AlphaGo? That system was also trained to predict human data initially yet it's competent to the point of beating most humans in Go.
> Weird you don't have this requirement for the OP spewing his urban myths above.
It isn't my purpose try to convince you that your apparent presumption that the output of a human and a machine are somehow equivalent and should be treated equally is wrong.
Why is an LLM more prone to hallucination than AlphaGo?
> It isn't my purpose try to convince you that your apparent presumption that the output of a human and a machine are somehow equivalent and should be treated equally is wrong.
You should judge arguments by their merits, not by who is saying them.
This data is from 2006. Over 20 years, there has been substantial progress in CT radiation reduction through model-based iterative reconstruction and now ML-assisted reconstruction, aside from iterative advances in detector sensitivity and now photon-counting CT.
In clinical practice, those doses are about 2-3x what I see on the machine dose reports every day at my place of work.
In thin patients who can hold still, I've done full-cycle cardiac CT and achieved a < 1 mSv dose. We are always trying to get the dose down while still being diagnostic.
Someone I know got partial constipation, lack of apetite and stomach reflux. After some month of triying to fix the reflux, they discovered it was intestine cancer when the cancer was big enough to block almost all the flow.
IIUC from a sibling reply, you already used a few laxative, so perhaps a CT scan was the next step.
I had a CT scan ordered for abdominal discomfort which had been making sleep a nightmare for years.
I started taking ag1 and Metamucil and the stomach discomfort has completely gone away over a span of weeks/months.
The resulting dramatic improvement in sleep cascades to just about everything in my life and different recurring health problems keep disappearing now.
It’s crazy how many problems can be caused by apparently just not getting enough fiber.
Never ended up getting the CT scan, which probably would’ve been expensive and involve some small degree of risk.
But did those words really get through to you like an energetic photon? I think, it's quite ionic how frequently the last strand has to break before we realize, we should have been radicalized by people, not high voltage discharge events.
I did try a boatload of OTC products, and eventually went to a generalist and then a specialist when it became severe and chronic. The OTC products recommend that on their labels. I now manage it with careful diet and a daily dose of polyethylene glycol.
If its any consolation, having diagnosed a malignant papilary or follicular thyroid tumor (surprizingly) is correlated with equal or slightly increased lifespan compared to the population that did not have this tumor—maybe it is because of having more frequent or better access to healthcare, which is harder to control in such epidemiological studies. It is one of the few positive known relationships with cancer.
Yup, this is something that shows up¹ for melanoma, thyroid, and prostate cancers: those who are diagnosed when the cancers are in situ (haven't left the tissue of origin) have better 5-year survival chances compared to people of the same age, race, and sex. Likely because, if people are diligent enough about their healthcare to report early warning signs and get the recommended screenings, those people also have much healthier lifestyles. If there were a way to control for lifestyle, I'd imagine the "benefit" would disappear or become a small but clear negative.
1: You won't find relative net survival above 100% in the CDC's statistics. That's because they calculate survival rates using daily differences in death hazards derived from life tables of people with cancer and those without. Add up the differences across all days, do some exponential math, and voila: relative net survival rates. But, if the relative risk for a day is negative (i.e. those without cancer have a higher risk of death), then they set the relative risk to 0 instead for that day. Which is ridiculous, IMO. It's forcing a distribution of actual events to match an idealized model.
Only after the procedure my ENT told me that if she were to pick a cancer to get it would be this one, and that the experts are trying to rename it from cancer to neoplasm because of its relative benignity. But I hadn't heard that it could actually be a positive. That underlines the mixed blessing of screening tests.
It also underlines the second-order risks of unneeded diagnostic screenings, even those that don’t include ionising radiation and its ilk, as the surgery you may otherwise have not had is itself not free from risk. Of course the case generalises out from there as well to not only this specific cancer.
I knew the math wasn't limited to 90 degree slices. I've had a few CT scans, and twice when I got my copy the DICOMs were a bunch of 90 degree TIFF slices. It wouldn't surprise me if the radiologist had the raw beam data and could slice it however they chose.
the Tiff slices is just post process storage. A good DICOM reader can view those tiffs in any direction.
After all, if you have the tiffs, you already know the grayscale for every pixel in the XYZ space. You just need to grab the right pixels from each slice
Interesting stuff! Could you suggest a DICOM reader that does so?
I had assumed slicing the raw beam data would give you much better output resolution whenever there were differences between transaxial and z resolution, since at some angle and offset you end up sampling across the largest gaps in the XYZ pixels. But maybe that's not a real issue? Is this how it's done in practice?
Things like this are why we don't run general screening for rare diseases.
The risk from screening, and the risks from further diagnosis and accidental treating of false positives can be much higher than the disease itself as long as it is rare enough.
I think your logic arrow is the wrong way around. We only run screening for rare diseases when indicated, and then get things like this.
If CT scans are performed on more than 5% * (1 + false positive rate) of suspected cancer cases, having a CT scan in the history of 5% of cancer cases is entirely expected.
This is what the healthcare community claims, but they're wrong.
I took a preventative MRI run by an ML/AI company that the healthcare folks say is a bad idea. I didn't discover any hidden cancers but they did find 1-2 emerging health issues that were preventable with simple diet and lifestyle changes.
If everyone showed up to their doctor asking for preventative imaging, it would overwhelm doctors since there aren't enough resources to treat everyone who is sick. Your individual health will always be less important than the integrity of the system.
No its literally just a statistics issue. Say you screen someone for a 1 in a million disease with a 0.001% false positive rate. If you find something and have to do a biopsy to figure out if its a real issue or not, you will have 99.9% of them be for nothing. Biopsies are actually risky procedures that can have dangerous complications that can and do harm people. Say your biopsy has a 99% accuracy. This means even after all that someone with a confirmed biopsy only has a 10% chance of having the disease, and may get dangerous and life changing treatment for nothing.
"The for-profit company's bullshit generator promised it helped me with some minor stuff" is perhaps not as compelling evidence as you imagine it to be.
At least one of the issues was a high definition image of a degenerating disc, a child could diagnose it by comparing it to the image of a healthy spine, never mind an algorithm.
You would have no idea you had it without imaging, since in the early stages you feel nothing.
Now I can work to build up muscle around that area and avoid over exerting that part of my back, instead of dealing with pain and being prescribed opiates in 20 years. Another example of how the system has killed countless people and absolutely failed the public.
Scott Alexander’s article on altruistic kidney donation weighed the initial CT scan as a heavy negative, like an incremental 1 in 650 risk of death. Shocking to me at the time, but the number seemed to check out, at least as a first order estimate.
Yuck, I have recurrent kidney stones and have had many CT-scans. It seems to have become the standard procedure when you complain of abdominal pain at the ER. Years ago I remember just getting an X-ray.
What's interesting is I needed surgery to remove the most recent stones, and I've not had a CT-scan since- the urologist uses ultrasound.
On the other hand, I've had fluoroscopy.. probably worse than even CT-scans.
The comments on that article heavily criticized that portion. I don't know jack about the topic, but it really did seem like just Scott's envelope-math against the sentiment of the entire field: "this is not enough radiation to matter".
I’ve gotten heart scans twice to monitor coronary artery calcification and get an Agatson score. I wonder how risky this is? I feel like the last time I did it the technician said that the amount of energy they have to use now is much less due to advances in CT scanning machines.
I guess a heart scan is about like six months of natural background radiation according to this chart.
To maybe oversimplify it, cancer risk from radiation is all a stats game. The situations where you get a CT scan is either very rare (once or twice in a lifetime and often highly localized) or for a very acute issue (eg a heart attack or car accident) that is almost certainly worth the risks.
Also, ionizing radiation has a varying risks to different tissues. "Soft" tissues that have cells that divide a lot (lungs, colon, etc) are of greater risk than others. I wouldn't bat much of an eye for a CT scan on my knee, but would be more worried about a chest procedure. Again, more worried doesn't mean I wouldn't do it, as the alternative is either a much more expensive MRI, much more fuzzy echo-cardiogram, or wondering if my health is more seriously at risk.
The science is based on assumptions and extrapolation, they drew a linear plot line between rates of cancers at different levels of radiation, and then extended it down and to the left. But there is no actual experimental data showing a relationship between low dose radiation and cancer (Ironically there IS evidence that rates of overall cancers are lower in high altitude cities like Denver with more background radiation).
Radiation risk assessment have been modernized less than DARE propaganda.
The Linear No-Threshold LNT hypothesis/model is still the fundament of all radiation protection theory and the modeling used in it.
The problem with using that is that since twenty years back we've known that both antioxidant activity and DNA-repair and protection mechanisms do not scale linearly.
Meaning that a more correct approximation of reality would be using a Non-Linear With-Threshold model.
But because our culture of permanent radiation hysteria we're paralyzed when it comes to changing the overarching guidelines, even when everyday practice have practically left it behind.
Well actually let’s find out whether they do cause it or not. Patients ought to know the risks beforehand if so.
The calculation as to net benefit can be done later.
Largely agree, but still very much depends on what you're screening for. For example, my oncologist still recommends CT over MRI for post-surgical screening as the increased resolution makes it possible to detect tumors a bit earlier.
I’m not familiar with the parameters of the machines readily available to your provider, but I can say that the risk/reward scenario for an intervention for someone coming out of cancer surgery is distinct. We give cancer patients chemo and radiation that we would never give to someone who just showed up in the ER or was still undergoing preliminary diagnostics.
You can very easily come up with reasonable plans to euthanise sub categories of the population to "save" lives if you only care about the total numbers of people surviving...
There can be big differences in radiation doses depending on the type of CT scanner used. Some radiology practices advertise low-dosage scanners [1]. So, if you need a CT scan you can ask for the dosage and find a practice that has a low-dosage scanner.
So 0.1% extra lifetime risk for every CT scan, I guess I went from 40% lifetime risk to 40.5, I guess I'll keep not drinking, not smoking and not being obese to help with the statistics.
Radiographer: “MRI (magnetic resonance imaging) creates detailed images of the inside of the body using strong magnetic fields and radio waves, rather than X-rays. MRI is/was the holy grail for medical imaging professionals. Arguably the coolest images come from MRI”
In my case, I had a lung issue and CT scans are more sensitive to air being where it shouldn't be. At least two of the 5 ct scans could probaly just have been x-rays tho.
Statistical topic are presented really poorly in the media.
If what the reader cares about is the risk to them, why is the proportion of all cancers caused by CT relevant? If we found a way to prevent 50% of all other cancers would CT become higher risk?
Stuff like this hits me in my health anxiety pretty bad, even if I know deep down that there's no point, on an individual scale, in worrying about this sort of thing; it's more of interest to clinicians for decision making. Still... I've had a couple CT scans with contrast in the past year, and that is probably somewhere around 20-25 mSv of radiation. In the grand scheme of things, it's really not that catastrophic of an amount, but it's a hell of a lot more than background radiation. Scary.
Makes me wonder if 10 mSv all at once is worse than 10 mSv over the course of a year. It seems that airline crews are only expected to be exposed to a dose from between 2 to 9 mSv annually[1], which makes a abdominal CT scan with contrast seem especially bad.
Of course, rationally speaking, I think at the individual level it's hard to really gauge this any more than any other residual risk factor. You could get very unlucky with cell damage from anything, more radiation just gives you more tickets to the lottery. I'm sure other factors play a role on an individual level and the risk to each person is not static.
I didn't read the JAMA article, but shouldn't it be possible to test that hypothesis differently? E.g., people get CT scans for fractures in knee or wrist. Cancer in those places is very rare, so of CT scans cause cancer, shouldn't there be noticeable difference between scanned and unscanned people?
That's my point: if CT scans cause cancer, cancer in the wrist or knee should be much more frequent among people who had a wrist or knee CT scan than among the general population. CT scans are relatively new, so there probably is a record in each patient's history.
Again, not necessarily. Different things cause different cancers. You're unlikely to get melanoma from smoking; you're unlikely to get liver cancer from a sunburn.
CTs may not cause significant amounts of wrist/knee cancer - I can't speak either way on that - but that wouldn't mean they're 100% safe elsewhere. For starters, wrist/knee imaging needs less radiation - they're relatively thin parts of the body, and relatively small regions.
But then the assumptions behind the article is not general, and the conclusions would have to amended to the radiation dosis and/or tissue. Which makes sense, of course.
MRI's themselves produce no cancer risk as they're not ionizing radiation. There's SOME questions about SOME of the dyes used for SOME MRI procedures, but those are usually used in situations where the alternative is worse - so do it.
MRI doesn't use ionising radiation so it's a stretch. Most likely cause would have to be some toxic effect of the contrast dye (as opposed to any sort of ionising radiation), but no compelling evidence exists for that.
MRI's magnetic field is not strong enough. CT scans use Röntgen radiation, and that's known to cause ionization (the waves can displace electrons), which --in DNA-- potentially causes cancer.
Depends. MRI itself is safe, but they often add "contrast" which is known to cause cancer (I'm not clear on if there is more than one choice for contrast though, or if they all cause cancer). Of course contrast is mostly used when they looking at a something - likely a tumor that might or might not be cancer to decide how to treat it - in that case does it matter that your long term cancer prospects go up when without it your short term prospects are not good.
There is no compelling evidence that MRI contrast agent causes cancer. Gadolinium (the stuff that’s in the contrast agent) can deposit in the body, e.g. in the brain, but if this even has any consequences is still unclear. Nonetheless there is some nice research going on how to drastically reduce the amount of contrast agent needs to be administered through image postprocessing.
CT scans are likely overused; my spouse has several chronic conditions and after receiving dozens a year for a while, we started asking if a CT was clinically indicated, or just precautionary. Mostly the response is "just in case". I wish EMRs did a better job of highlighting how many CTs someone's had recently for this sort of decision making.
There've also long been problems with kids getting unnecessarily high adult doses of radiation. My dad's a peds radiologist and was heavily involved in the founding of https://www.imagegently.org/.
My kid needed an abdominal ultrasound in the ER, but the ultrasonographer had gone home for the night. They did a CT instead, despite my concerns. CT missed the problem, which festered for several more years before being discovered during our next ER visit … on an ultrasound.
The "almost certainly" that you brush off is the entire point of the calculation. Is it 95% certain or 99.5% certain? The exact balance between benefit and risk in medical procedures is exactly how it is determined when to use them in the standard of care.
My first MRI about 30 years ago they did a precautionary CAT scan of my head because I had worked in machine shop (the place I worked had a machine shop and I used it for small personal projects), dunno if they do that anymore, but I was told ferrous bits in eyes had led to disastrous results for at least one patient.
Yeah, no. A doctor that I had a feeling wasn't paying too close attention to what I was saying ordered a pelvic/abdominal CT with and without contrast, ~30-40 mSv. Nothing turned up on the scans. When I went back he said "nothing's wrong" and, confused, I described my symptoms again. He just said "Oh! You need physical therapy."
Two weeks of physical therapy and I was fine.
At the time I was mad about the money, now I'm just thinking "what a dumb way to (maybe) get gut cancer."
I was young. I thought I was scheduled for an MRI like the one I had for my sinuses. I didn't even know what a was CT at the time.
On the other side of the coin, my always healthy dad did 6 weeks of physical therapy for hip joint pain that turned out to be cancer, which was immediately detected when they finally decided to perform a CT scan. He passed away almost exactly 1 year later at 46 years old.
Thanks, and I was trying to highlight the challenges of any situation like this. I do agree with the fundamental premise that we need to get better and deciding when to scan and coming up with non(or less) destructive techniques.
Protip: Taking Vitamin C or E orally before a scan can significantly reduce the amount of damaged DNA in your system, potentially reducing your cancer risk. There are several studies on Pubmed indicating this.
I have had a lot of stomach issues, I have done 3 CT scans during my life and I am not even 40 years old. I worry already about the dosage I have gotten.
Though when I asked they said it was like a long flight trip to aroynd the globe. While I don't believe that, I do believe that they are much more effective than they were 10+ years ago. Also I wouldn't have got my stomach surgery without my first one.
Theoretically causing a lot of cancers in modelling studies.
In practice a CT machine is also a much better workhorse for innumerable tasks that are very hard to effectively investigate with an MR machine, as MR imaging takes significantly more time, and requires more technical knowhow among the medical staff involved.
If this were true, we should be seeing a detectable, statistically significant higher rate of cancer in Japan, which has by far the highest rate of CT machines per person. (almost 3× that of the USA, which is still high even among high-income countries)
Considering the health and life expectancy in Japan, I call BS.
The load factor would need to be lower than one third of the US to balance it out, which I'd claim is quite unlikely.
And yeah of course it's multifactorial. It'd make more sense to look at cancer data specifically, but I don't have that at hand. However, cancer is a leading factor in lifespan limits…
Impossible to draw any conclusions from such a convoluted and problematic model. No mention of how they determined patients were unique, or whether multiple scans were counted for a single patient. No mention of patient data - seems that covariates were estimated, leading to greater uncertainty. For example, we have no idea if any of these patients already had cancer before getting a scan. And of course, this entire model is incapable of answering the question that patients actually care about: not "will I get cancer from this?" but "will this scan more likely increase or decrease my lifespan and/or quality of life?".
Seems pretty common sense to me that you're gonna have more people with hidden cancers coming in to get CT for phantom pains, etc and later discover they had cancer all along. That doesn't mean CT caused it. Did the study control for this?
> Did the study control for this?
No, because that's not how the study worked, i.e. it wasn't actually tallying cancer rates from people who had CTs. It basically just looked at the amount of radiation that a CT scan gives a person, and then extrapolated the cancer that would be expected from that radiation dose based on other data we have of e.g. people exposed to radiation in their jobs, and nuclear fallout occurrences.
Previous studies I've read did account for this, and put the number at about 3%. That said CT manufacturers have been working on a bunch of technology to make this better, either by doing a better job at not aiming at sensitive areas or by reducing the amount of radiation needed to get the same resolution in the images.
The whole dataset seems like something hard to work with, population that needs CT scan in the first place is very biased, people don't do CT scans for fun but because there is something weird that docs can't explain already.
It's unclear to me whether you read the journal article or just the Ars article? If you're referring to the journal article that gives your assessment much more weight.
[dead]
I went to the doctor complaining of constipation. He sent me for a CT scan which showed that I was literally full of shit. The prescription was for a large dose of MiraLax. Now I wonder if the risk of the CT scan was really justified given that plenty of people already tell me that for free and without radiation.
A. Newer CT scan machines use lower radiation doses.
B. If you're getting only one scan a year you're fine and within yearly limits of radiation dosage considered acceptable.
Remember that you'll get comparable levels of radiation even if you commute through the grand central station every day.
This paper is for lack of a better word, crap. It's becoming sensational for the conclusion it makes and I'm afraid it's now going to create more harm because of that.
> B. If you're getting only one scan a year you're fine and within yearly limits of radiation dosage considered acceptable.
But doesn't it make a difference if that "acceptable yearly limit" is spread out throughout the year as opposed to a few minutes of CT scan session?
Yes, the term is DDREF - Dose and Dose Rate Effectiveness Factor.
I really don’t buy it if someone says the opposite.
Tf is going on in Grand Central?
Granite.
I had a CT of my pelvis and abdomen recently and worked out it was equivalent to about 5 years worth of background radiation.
The dose required is actually quite a lot higher than typical comparisons to eg chest X-rays and the like
What about contrast? I've heard it's really hard on your thyroid.
This isn't thorotrast we're talking about.
> Remember that you'll get comparable levels of radiation even if you commute through the grand central station every day.
Gemini says this:
> A single typical CT scan delivers a dose that is roughly 1,000 to over 5,000 times higher than the dose you'd get from spending a few hours in Grand Central Terminal.
Where did you get that from?
If the hallucination machine can cite a source, check and cite that for facts, but don't cite the hallucination machine.
Weird you don't have this requirement for the OP spewing his urban myths above.
Human hallucinations are natural.
Machine hallucinations are avoidable.
Was it hallucinating here, or are the commenters hallucinating? What OP is saying is just not true. A CT scan and normal daily commute in Grand Central station are NOT comparable in terms of radiation received. Somehow this is controversial because an AI said it?
The machine appears to have hallucinated the incomparable comparison, instead of a human.
(And I'm not picking on the machine at all here. I use it all the time. At first, I used to treat it like an idiot intern that shouldn't have been hired at all: Creative and full of spirit, but untrustworthy and all ideas need to be filtered. But lately, it's more like an decent apprentice who has a hangover and isn't thinking straight today. The machine has been getting better as time presses on, but it still goes rather aloof from time to time.)
I don't understand how was the machine hallucinating?
Are you new to LLMs?
They hallucinate shit all the time. It might even be said that all LLM output is a hallucination (but some of these hallucinations are useful).
It was NOT hallucinating this time. OP was.
What do you mean all LLM output is hallucination? Would you say the same about AlphaGo? That system was also trained to predict human data initially yet it's competent to the point of beating most humans in Go.
Is AlphaGo an LLM?
Anyway, we were here:
> Weird you don't have this requirement for the OP spewing his urban myths above.
It isn't my purpose try to convince you that your apparent presumption that the output of a human and a machine are somehow equivalent and should be treated equally is wrong.
So I won't.
Why is an LLM more prone to hallucination than AlphaGo?
> It isn't my purpose try to convince you that your apparent presumption that the output of a human and a machine are somehow equivalent and should be treated equally is wrong.
You should judge arguments by their merits, not by who is saying them.
You should have arguments, not gish gallops.
I'm out.
The LLM had the argument that OP's comparison was off. Which you would see if you didn't have a stick up your arse about AI.
Did you actually discredit someone or have you not properly considered your units in this response?
Commute through the Grand Central station everyday is certainly not a few hours.
And people don't tend to get a CT scan very frequently so the timeline here is massive.
In your opinion how many hours spent in Grand Central station equal the radiation received from a CT scan?
Somewhere between 7 and 700 days.
CT Scan: 10-1000 mrem
Grand Central Station: 525 mrem / yr
https://files.eric.ed.gov/fulltext/ED297952.pdf
So OP's statement is true for people who live IN the station.
It's roughly 40 min per workday over a typical year. That's a bit high but not unreasonably so.
That would amount to 10 mrem of radiation per year. I don't believe this is a realistic estimate for a CT scan though. From epa.gov [1]:
- Head CT: 2.0 mSv (200 mrem)
- Chest CT: 8.0 mSv (800 mrem)
- Abdomen CT: 10 mSv (1,000 mrem)
- Pelvis CT: 10 mSv (1,000 mrem)
So for a head CT, one would need to spend more than 13 hours per workday in the station. OP was off at least an order of magnitude.
https://www.epa.gov/radiation/frequent-questions-radiation-m...
This data is from 2006. Over 20 years, there has been substantial progress in CT radiation reduction through model-based iterative reconstruction and now ML-assisted reconstruction, aside from iterative advances in detector sensitivity and now photon-counting CT.
In clinical practice, those doses are about 2-3x what I see on the machine dose reports every day at my place of work.
In thin patients who can hold still, I've done full-cycle cardiac CT and achieved a < 1 mSv dose. We are always trying to get the dose down while still being diagnostic.
Source: Practicing radiologist.
Fair enough. That was the first number I pulled from Google, but I trust your source a good deal more.
I used the word comparable. Given they are in the same ballpark of log scale i stand vindicated in my opinion.
Also there's an apple store there. RIP all the geniuses there i suppose
So if you pass through GCT every day it does become comparable to a CT scan?
Someone I know got partial constipation, lack of apetite and stomach reflux. After some month of triying to fix the reflux, they discovered it was intestine cancer when the cancer was big enough to block almost all the flow.
IIUC from a sibling reply, you already used a few laxative, so perhaps a CT scan was the next step.
I had a CT scan ordered for abdominal discomfort which had been making sleep a nightmare for years.
I started taking ag1 and Metamucil and the stomach discomfort has completely gone away over a span of weeks/months.
The resulting dramatic improvement in sleep cascades to just about everything in my life and different recurring health problems keep disappearing now.
It’s crazy how many problems can be caused by apparently just not getting enough fiber.
Never ended up getting the CT scan, which probably would’ve been expensive and involve some small degree of risk.
pro-tip: start your days with an unripe banana, at least slightly greenish. If it's sweet it's too ripe for medicinal value.
Beats any processed supplement or other OTC drugs IME.
But did those words really get through to you like an energetic photon? I think, it's quite ionic how frequently the last strand has to break before we realize, we should have been radicalized by people, not high voltage discharge events.
Why would you go to the doctor for that instead of first trying one of the many known solutions?
* a tablespoon of epsom salt * a tablespoon of mineral oil * several OTC products
I did try a boatload of OTC products, and eventually went to a generalist and then a specialist when it became severe and chronic. The OTC products recommend that on their labels. I now manage it with careful diet and a daily dose of polyethylene glycol.
Yeah, a plain old abdominal x-ray might've sufficed to diagnose that.
Or the pre-x-ray technique of abdominal palpation.
The same scan found a large goiter which led to surgical removal of a malignant thyroid tumor. So I have mixed feelings.
If its any consolation, having diagnosed a malignant papilary or follicular thyroid tumor (surprizingly) is correlated with equal or slightly increased lifespan compared to the population that did not have this tumor—maybe it is because of having more frequent or better access to healthcare, which is harder to control in such epidemiological studies. It is one of the few positive known relationships with cancer.
Yup, this is something that shows up¹ for melanoma, thyroid, and prostate cancers: those who are diagnosed when the cancers are in situ (haven't left the tissue of origin) have better 5-year survival chances compared to people of the same age, race, and sex. Likely because, if people are diligent enough about their healthcare to report early warning signs and get the recommended screenings, those people also have much healthier lifestyles. If there were a way to control for lifestyle, I'd imagine the "benefit" would disappear or become a small but clear negative.
1: You won't find relative net survival above 100% in the CDC's statistics. That's because they calculate survival rates using daily differences in death hazards derived from life tables of people with cancer and those without. Add up the differences across all days, do some exponential math, and voila: relative net survival rates. But, if the relative risk for a day is negative (i.e. those without cancer have a higher risk of death), then they set the relative risk to 0 instead for that day. Which is ridiculous, IMO. It's forcing a distribution of actual events to match an idealized model.
Only after the procedure my ENT told me that if she were to pick a cancer to get it would be this one, and that the experts are trying to rename it from cancer to neoplasm because of its relative benignity. But I hadn't heard that it could actually be a positive. That underlines the mixed blessing of screening tests.
It also underlines the second-order risks of unneeded diagnostic screenings, even those that don’t include ionising radiation and its ilk, as the surgery you may otherwise have not had is itself not free from risk. Of course the case generalises out from there as well to not only this specific cancer.
Sounds like the CT scan was a clear win then.
An abdominal CT found a goiter?
They did chest too because I also had some higher up pain on my side. That also resolved with the bowel flush.
Same. The CT is to rule out diverticulitis and in my case, since the pain was located in my lower right abdomen, appendicitis.
I was just full of shit, as usual. Now I eat salads and drink more water when I am at elevation.
why a CT and not a X-ray? did they need to see the gestating turds in 3D?
not a doctor, but a CT could show mechanical obstruction or twisted intestines in a way X-ray would not.
I imagine the doctor already assumed the shit was there, but wanted to understand why.
I further imagine prescribing a megadose of laxative might be harmful if someone cant expel the shit.
I really wonder if there's value in straightening the tract in post. Sometimes something at 45 degrees doesn't really view well in the slices.
CT isnt constrained to 90 degree slices and can be viewed at any arbitrary angle, or in 3D without further processing.
This video [1] is a presentation on bowel CT with great images. For those interested in X-ray, compare the X-rays at 14 minutes with the CT at 10.
Also worth noting, that X-ray is being recommended as a quick diagnostic before moving to CT
https://youtu.be/ZvDOkrn2ygQ?t=630
I knew the math wasn't limited to 90 degree slices. I've had a few CT scans, and twice when I got my copy the DICOMs were a bunch of 90 degree TIFF slices. It wouldn't surprise me if the radiologist had the raw beam data and could slice it however they chose.
the Tiff slices is just post process storage. A good DICOM reader can view those tiffs in any direction.
After all, if you have the tiffs, you already know the grayscale for every pixel in the XYZ space. You just need to grab the right pixels from each slice
Interesting stuff! Could you suggest a DICOM reader that does so?
I had assumed slicing the raw beam data would give you much better output resolution whenever there were differences between transaxial and z resolution, since at some angle and offset you end up sampling across the largest gaps in the XYZ pixels. But maybe that's not a real issue? Is this how it's done in practice?
lol. Well executed.
Things like this are why we don't run general screening for rare diseases.
The risk from screening, and the risks from further diagnosis and accidental treating of false positives can be much higher than the disease itself as long as it is rare enough.
I think your logic arrow is the wrong way around. We only run screening for rare diseases when indicated, and then get things like this.
If CT scans are performed on more than 5% * (1 + false positive rate) of suspected cancer cases, having a CT scan in the history of 5% of cancer cases is entirely expected.
This is what the healthcare community claims, but they're wrong.
I took a preventative MRI run by an ML/AI company that the healthcare folks say is a bad idea. I didn't discover any hidden cancers but they did find 1-2 emerging health issues that were preventable with simple diet and lifestyle changes.
If everyone showed up to their doctor asking for preventative imaging, it would overwhelm doctors since there aren't enough resources to treat everyone who is sick. Your individual health will always be less important than the integrity of the system.
No its literally just a statistics issue. Say you screen someone for a 1 in a million disease with a 0.001% false positive rate. If you find something and have to do a biopsy to figure out if its a real issue or not, you will have 99.9% of them be for nothing. Biopsies are actually risky procedures that can have dangerous complications that can and do harm people. Say your biopsy has a 99% accuracy. This means even after all that someone with a confirmed biopsy only has a 10% chance of having the disease, and may get dangerous and life changing treatment for nothing.
> they did find 1-2 emerging health issues that were preventable with simple diet and lifestyle changes
Sounds like the exact same results you'd have gotten without imaging.
"The for-profit company's bullshit generator promised it helped me with some minor stuff" is perhaps not as compelling evidence as you imagine it to be.
At least one of the issues was a high definition image of a degenerating disc, a child could diagnose it by comparing it to the image of a healthy spine, never mind an algorithm.
You would have no idea you had it without imaging, since in the early stages you feel nothing.
Now I can work to build up muscle around that area and avoid over exerting that part of my back, instead of dealing with pain and being prescribed opiates in 20 years. Another example of how the system has killed countless people and absolutely failed the public.
> You would have no idea you had it without imaging, since in the early stages you feel nothing.
From 30 years of age, disc degeneration is more likely than not. You don’t need a scan to tell you you’re in the early stages of it.
By age 50, around 80% of people have a degenerative disc on imaging... it's over 1/3rd by age 20.
Everyone is going to get a bad back at some point if they don't take care of themselves.
"Eat right and exercise " is very generic advice, but it's cheaper than an MRI and will prevent more disease.
Scott Alexander’s article on altruistic kidney donation weighed the initial CT scan as a heavy negative, like an incremental 1 in 650 risk of death. Shocking to me at the time, but the number seemed to check out, at least as a first order estimate.
Yuck, I have recurrent kidney stones and have had many CT-scans. It seems to have become the standard procedure when you complain of abdominal pain at the ER. Years ago I remember just getting an X-ray.
What's interesting is I needed surgery to remove the most recent stones, and I've not had a CT-scan since- the urologist uses ultrasound.
On the other hand, I've had fluoroscopy.. probably worse than even CT-scans.
The comments on that article heavily criticized that portion. I don't know jack about the topic, but it really did seem like just Scott's envelope-math against the sentiment of the entire field: "this is not enough radiation to matter".
I’ve gotten heart scans twice to monitor coronary artery calcification and get an Agatson score. I wonder how risky this is? I feel like the last time I did it the technician said that the amount of energy they have to use now is much less due to advances in CT scanning machines.
I guess a heart scan is about like six months of natural background radiation according to this chart.
https://www.radiologyinfo.org/en/info/safety-xray
My father’s side has a history of heart attacks, so I’m trying to avoid that fate and consider the risks worth it.
To maybe oversimplify it, cancer risk from radiation is all a stats game. The situations where you get a CT scan is either very rare (once or twice in a lifetime and often highly localized) or for a very acute issue (eg a heart attack or car accident) that is almost certainly worth the risks.
Also, ionizing radiation has a varying risks to different tissues. "Soft" tissues that have cells that divide a lot (lungs, colon, etc) are of greater risk than others. I wouldn't bat much of an eye for a CT scan on my knee, but would be more worried about a chest procedure. Again, more worried doesn't mean I wouldn't do it, as the alternative is either a much more expensive MRI, much more fuzzy echo-cardiogram, or wondering if my health is more seriously at risk.
Radiation is poorly understood in healthcare due to the LNT Model https://en.wikipedia.org/wiki/Linear_no-threshold_model.
The science is based on assumptions and extrapolation, they drew a linear plot line between rates of cancers at different levels of radiation, and then extended it down and to the left. But there is no actual experimental data showing a relationship between low dose radiation and cancer (Ironically there IS evidence that rates of overall cancers are lower in high altitude cities like Denver with more background radiation).
I’ve remodulated my phaser arrays and randomized the stochastic spectral frequencies ten times, but those Borg keep adapting!!1
Radiation risk assessment have been modernized less than DARE propaganda.
The Linear No-Threshold LNT hypothesis/model is still the fundament of all radiation protection theory and the modeling used in it.
The problem with using that is that since twenty years back we've known that both antioxidant activity and DNA-repair and protection mechanisms do not scale linearly.
Meaning that a more correct approximation of reality would be using a Non-Linear With-Threshold model.
But because our culture of permanent radiation hysteria we're paralyzed when it comes to changing the overarching guidelines, even when everyday practice have practically left it behind.
How many lives did those CT scans save vs. how many lives were lost due to the additional cancer cases they caused? That's the question, isn't it?
Well actually let’s find out whether they do cause it or not. Patients ought to know the risks beforehand if so. The calculation as to net benefit can be done later.
X-ray radiation causes cancer.
CT scanners don’t use magic non-carcinogenic x-rays.
Socrates is a man, men are mortal, Socrates is mortal.
We have the technology. We should have moved on to MRIs for nearly all scans years ago.
They're not interchangeable. CT scans have better resolution, take significantly less time, and are generally sensitive to different things.
You’re absolutely right, they’re not interchangeable. MRIs are better suited for soft tissues.
If you’re looking for a broken bone, take a single x-ray image instead of a whole CT scan, which is a far higher dose of X-ray radiation.
Largely agree, but still very much depends on what you're screening for. For example, my oncologist still recommends CT over MRI for post-surgical screening as the increased resolution makes it possible to detect tumors a bit earlier.
I’m not familiar with the parameters of the machines readily available to your provider, but I can say that the risk/reward scenario for an intervention for someone coming out of cancer surgery is distinct. We give cancer patients chemo and radiation that we would never give to someone who just showed up in the ER or was still undergoing preliminary diagnostics.
I mean you can't when a non-insignificant amount of people have magnetic metal in their body.
Please elaborate?
People get weird when using math to calculate human lives.
As they should. It’s not difficult to use questionable math to justify very awful things.
You can very easily come up with reasonable plans to euthanise sub categories of the population to "save" lives if you only care about the total numbers of people surviving...
There can be big differences in radiation doses depending on the type of CT scanner used. Some radiology practices advertise low-dosage scanners [1]. So, if you need a CT scan you can ask for the dosage and find a practice that has a low-dosage scanner.
[1] See, e.g., https://zwangerpesiri.com/services/ct/ (no affiliation; just an example).
So 0.1% extra lifetime risk for every CT scan, I guess I went from 40% lifetime risk to 40.5, I guess I'll keep not drinking, not smoking and not being obese to help with the statistics.
Medicine: first, do no harm.
Why not use MRIs since they skip the problem entirely?
Don’t say cost or supply. That’s just because CT scans, misguidedly, have more demand. More demand for MRIs would unlock savings from scale.
You can do a brain CT to detect a stroke in about 5 minutes. An MRI takes 30-60 minutes. Both useful but in emergency medicine you need the speed.
Drive more demand for MRIs and they’ll get faster too
They'll always be slower than CT scans because physics.
Is the theoretical physical speed limit higher or lower than what is relevant for most clinical use cases?
CT scans are better in a lot of ways. They're faster, higher resolution, and sensitive to different stuff than MRIs.
Radiographer: “MRI (magnetic resonance imaging) creates detailed images of the inside of the body using strong magnetic fields and radio waves, rather than X-rays. MRI is/was the holy grail for medical imaging professionals. Arguably the coolest images come from MRI”
https://radiographermedia.substack.com/p/x-ray-vs-ct-vs-mri
The coolest images come from MRI. Unquestionably.
In my case, I had a lung issue and CT scans are more sensitive to air being where it shouldn't be. At least two of the 5 ct scans could probaly just have been x-rays tho.
You can get an ultra fast CT scan and to a video of blood flow through your heart arteries.
I never saw that available via MRI.
Statistical topic are presented really poorly in the media.
If what the reader cares about is the risk to them, why is the proportion of all cancers caused by CT relevant? If we found a way to prevent 50% of all other cancers would CT become higher risk?
Stuff like this hits me in my health anxiety pretty bad, even if I know deep down that there's no point, on an individual scale, in worrying about this sort of thing; it's more of interest to clinicians for decision making. Still... I've had a couple CT scans with contrast in the past year, and that is probably somewhere around 20-25 mSv of radiation. In the grand scheme of things, it's really not that catastrophic of an amount, but it's a hell of a lot more than background radiation. Scary.
> but it's a hell of a lot more than background radiation. Scary.
Not if you fly decent distances a dozen times a year or more.
Makes me wonder if 10 mSv all at once is worse than 10 mSv over the course of a year. It seems that airline crews are only expected to be exposed to a dose from between 2 to 9 mSv annually[1], which makes a abdominal CT scan with contrast seem especially bad.
Of course, rationally speaking, I think at the individual level it's hard to really gauge this any more than any other residual risk factor. You could get very unlucky with cell damage from anything, more radiation just gives you more tickets to the lottery. I'm sure other factors play a role on an individual level and the risk to each person is not static.
[1]: https://pmc.ncbi.nlm.nih.gov/articles/PMC9447865/#:~:text=Pi...
5% is such a massive number that the FDA would shut down non-ER CT scans if it were true. I point you to the replication crisis.
https://en.wikipedia.org/wiki/Replication_crisis
I didn't read the JAMA article, but shouldn't it be possible to test that hypothesis differently? E.g., people get CT scans for fractures in knee or wrist. Cancer in those places is very rare, so of CT scans cause cancer, shouldn't there be noticeable difference between scanned and unscanned people?
It's quite hard to give bones and joints cancer. Cancer prefers dividing cells.
Some blood cells are produced in bone marrow and it's not rare to get "bone cancer".
Yup, but it's significantly less common than most other forms of cancer.
If cancer is also rare in those spots without a CT, that would seem to indicate a major confounding variable at play.
That's my point: if CT scans cause cancer, cancer in the wrist or knee should be much more frequent among people who had a wrist or knee CT scan than among the general population. CT scans are relatively new, so there probably is a record in each patient's history.
Again, not necessarily. Different things cause different cancers. You're unlikely to get melanoma from smoking; you're unlikely to get liver cancer from a sunburn.
CTs may not cause significant amounts of wrist/knee cancer - I can't speak either way on that - but that wouldn't mean they're 100% safe elsewhere. For starters, wrist/knee imaging needs less radiation - they're relatively thin parts of the body, and relatively small regions.
But then the assumptions behind the article is not general, and the conclusions would have to amended to the radiation dosis and/or tissue. Which makes sense, of course.
What about MRI? Just had one. Sorry if it's a stupid question, I don't know much about this
MRI's themselves produce no cancer risk as they're not ionizing radiation. There's SOME questions about SOME of the dyes used for SOME MRI procedures, but those are usually used in situations where the alternative is worse - so do it.
MRI doesn't use ionising radiation so it's a stretch. Most likely cause would have to be some toxic effect of the contrast dye (as opposed to any sort of ionising radiation), but no compelling evidence exists for that.
MRI's magnetic field is not strong enough. CT scans use Röntgen radiation, and that's known to cause ionization (the waves can displace electrons), which --in DNA-- potentially causes cancer.
Depends. MRI itself is safe, but they often add "contrast" which is known to cause cancer (I'm not clear on if there is more than one choice for contrast though, or if they all cause cancer). Of course contrast is mostly used when they looking at a something - likely a tumor that might or might not be cancer to decide how to treat it - in that case does it matter that your long term cancer prospects go up when without it your short term prospects are not good.
There is no compelling evidence that MRI contrast agent causes cancer. Gadolinium (the stuff that’s in the contrast agent) can deposit in the body, e.g. in the brain, but if this even has any consequences is still unclear. Nonetheless there is some nice research going on how to drastically reduce the amount of contrast agent needs to be administered through image postprocessing.
Hmm. When I check a few years ago what looked like authortive people said it was - I will admit to not being an expert though.
citation?
You're safe
by the time you are scheduled to get a CT scan, the possible diagnosis which lead to the CT scan is almost certainly riskier than the cancer.
Move along...
No, not necessarily.
CT scans are likely overused; my spouse has several chronic conditions and after receiving dozens a year for a while, we started asking if a CT was clinically indicated, or just precautionary. Mostly the response is "just in case". I wish EMRs did a better job of highlighting how many CTs someone's had recently for this sort of decision making.
There've also long been problems with kids getting unnecessarily high adult doses of radiation. My dad's a peds radiologist and was heavily involved in the founding of https://www.imagegently.org/.
My kid needed an abdominal ultrasound in the ER, but the ultrasonographer had gone home for the night. They did a CT instead, despite my concerns. CT missed the problem, which festered for several more years before being discovered during our next ER visit … on an ultrasound.
The folks round these parts that transfuse the blood of young healthy people to boost their lifespan are probably having a regular CT scan too.
I don’t think they roam among us “plebs”
With the advent of these modern medical breakthroughs I believe we have been rebranded from "plebs" to "blood bags".
I have a friend who went to an allergist last week for sinus issues. They did a CT scan within 5 minutes of coming into the office.
If it's any consolation, a sinus CT is tuned to have a very low radiation dose compared to typical body CT scans.
The "almost certainly" that you brush off is the entire point of the calculation. Is it 95% certain or 99.5% certain? The exact balance between benefit and risk in medical procedures is exactly how it is determined when to use them in the standard of care.
My first MRI about 30 years ago they did a precautionary CAT scan of my head because I had worked in machine shop (the place I worked had a machine shop and I used it for small personal projects), dunno if they do that anymore, but I was told ferrous bits in eyes had led to disastrous results for at least one patient.
In most cases instead of CT scan one could do the same diagnosis with MRI scan, which is only a bit more expensive.
The MRI scan takes 10x longer, uses helium (of which there isn't an infinite supply) and can't be used on people with certain implants.
Yeah, no. A doctor that I had a feeling wasn't paying too close attention to what I was saying ordered a pelvic/abdominal CT with and without contrast, ~30-40 mSv. Nothing turned up on the scans. When I went back he said "nothing's wrong" and, confused, I described my symptoms again. He just said "Oh! You need physical therapy."
Two weeks of physical therapy and I was fine.
At the time I was mad about the money, now I'm just thinking "what a dumb way to (maybe) get gut cancer."
I was young. I thought I was scheduled for an MRI like the one I had for my sinuses. I didn't even know what a was CT at the time.
On the other side of the coin, my always healthy dad did 6 weeks of physical therapy for hip joint pain that turned out to be cancer, which was immediately detected when they finally decided to perform a CT scan. He passed away almost exactly 1 year later at 46 years old.
I don't like this coin. Sorry about your dad.
Thanks, and I was trying to highlight the challenges of any situation like this. I do agree with the fundamental premise that we need to get better and deciding when to scan and coming up with non(or less) destructive techniques.
Yeah, I got your meaning. Very well put.
[dead]
Protip: Taking Vitamin C or E orally before a scan can significantly reduce the amount of damaged DNA in your system, potentially reducing your cancer risk. There are several studies on Pubmed indicating this.
This arstechnica article is pretty good, but in my opinion the best article covering this study was published by NPR
http://npr.org/sections/shots-health-news/2025/04/16/g-s1-60...
I have had a lot of stomach issues, I have done 3 CT scans during my life and I am not even 40 years old. I worry already about the dosage I have gotten.
Though when I asked they said it was like a long flight trip to aroynd the globe. While I don't believe that, I do believe that they are much more effective than they were 10+ years ago. Also I wouldn't have got my stomach surgery without my first one.
It should be obvious that using the intense amount of ionizing radiation that CT scans use that of course they're causing a lot of cancer.
It's a shame our medical systems invested so heavily into CT machines at the expense of MRI's
Theoretically causing a lot of cancers in modelling studies.
In practice a CT machine is also a much better workhorse for innumerable tasks that are very hard to effectively investigate with an MR machine, as MR imaging takes significantly more time, and requires more technical knowhow among the medical staff involved.
Would you be able to see this effect comparing Americans and Canadians, assuming Canadians have way fewer CT scans on average?
If this were true, we should be seeing a detectable, statistically significant higher rate of cancer in Japan, which has by far the highest rate of CT machines per person. (almost 3× that of the USA, which is still high even among high-income countries)
Considering the health and life expectancy in Japan, I call BS.
Is the load factor of those Japanese machines similar to those used in the US? Isn't life expectancy multifactorial?
The load factor would need to be lower than one third of the US to balance it out, which I'd claim is quite unlikely.
And yeah of course it's multifactorial. It'd make more sense to look at cancer data specifically, but I don't have that at hand. However, cancer is a leading factor in lifespan limits…
Experts did not yet found that the mRNA Spike Vax causes cancer.