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CT scans could cause 5% of cancers, study finds; experts note uncertainty
- Zezima 2y agoby 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...
- cowfarts 2y ago[dead]
- blitzar 2y agoThe folks round these parts that transfuse the blood of young healthy people to boost their lifespan are probably having a regular CT scan too.
- chr1 2y agoIn most cases instead of CT scan one could do the same diagnosis with MRI scan, which is only a bit more expensive.
- ChocolateGod 2y agoThe 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.
- ceejayoz 2y agoNo, 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/ https://www.imagegently.org/.
- AyyEye 2y agoI 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.
- queuebert 2y agoIf it's any consolation, a sinus CT is tuned to have a very low radiation dose compared to typical body CT scans.
- queuebert 2y agoThe "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.
- el_benhameen 2y agoMy 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.
- miiiiiike 2y agoYeah, 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.
- fatnoah 2y agoOn 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.
- miiiiiike 2y agoI don't like this coin. Sorry about your dad.
- stevenwoo 2y agoMy 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.
- Tepix 2y agoHow 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?
- xeornet 2y agoWell 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.
- odyssey7 2y agoX-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.
- oyashirochama 2y agoI mean you can't when a non-insignificant amount of people have magnetic metal in their body.
- liamwire 2y agoPlease elaborate?
- itishappy 2y agoThey're not interchangeable. CT scans have better resolution, take significantly less time, and are generally sensitive to different things.
- odyssey7 2y agoYou’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.
- TaupeRanger 2y agoImpossible 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?".
- ashleyn 2y agoSeems 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?
- tedivm 2y agoPrevious 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.
- hn_throwaway_99 2y ago> 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.
- mirekrusin 2y agoThe 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.
- Mistletoe 2y agoI’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 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.
- AStonesThrow 2y agoI’ve remodulated my phaser arrays and randomized the stochastic spectral frequencies ten times, but those Borg keep adapting!!1
- hylaride 2y agoTo 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.
- oceanplexian 2y agoRadiation is poorly understood in healthcare due to the LNT Model https://en.wikipedia.org/wiki/Linear_no-threshold_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).
- sakex 2y agoWhat about MRI? Just had one. Sorry if it's a stupid question, I don't know much about this
- petters 2y agoYou're safe
- ashleyn 2y agoMRI 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.
- tgv 2y agoMRI'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.
- bluGill 2y agoDepends. 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.
- mthomasmw 2y agocitation?
- rasmus1610 2y agoThere 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.
- enjoytheview 2y agoSo 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.
- odyssey7 2y agoMedicine: 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.
- readthenotes1 2y agoYou 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.
- itishappy 2y agoCT scans are better in a lot of ways. They're faster, higher resolution, and sensitive to different stuff than MRIs.
- odyssey7 2y agoRadiographer: “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 https://radiographermedia.substack.com/p/x-ray-vs-ct-vs-mri
- itishappy 2y agoThe coolest images come from MRI. Unquestionably.
- qgin 2y agoYou 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.
- tgv 2y agoI 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?
- ceejayoz 2y agoIf cancer is also rare in those spots without a CT, that would seem to indicate a major confounding variable at play.
- tgv 2y agoThat'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.
- ceejayoz 2y agoAgain, 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.
- tgv 2y agoBut 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.
- itishappy 2y agoIt's quite hard to give bones and joints cancer. Cancer prefers dividing cells.
- daedrdev 2y agoThings 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.
- eqvinox 2y agoI 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.
- oceanplexian 2y agoThis 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.
- ceejayoz 2y ago"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.
- oceanplexian 2y agoAt 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.
- canadiantim 2y agoIt 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
- justlikereddit 2y agoTheoretically 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.
- delichon 2y agoI 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.
- ceejayoz 2y agoYeah, a plain old abdominal x-ray might've sufficed to diagnose that. Or the pre-x-ray technique of abdominal palpation.
- delichon 2y agoThe same scan found a large goiter which led to surgical removal of a malignant thyroid tumor. So I have mixed feelings.
- ceejayoz 2y agoAn abdominal CT found a goiter?
- delichon 2y agoThey did chest too because I also had some higher up pain on my side. That also resolved with the bowel flush.
- MaKey 2y agoSounds like the CT scan was a clear win then.
- pama 2y agoIf 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.
- sebastian_z 2y agoThere 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/ https://zwangerpesiri.com/services/ct/ (no affiliation; just an example).
- kristjansson 2y agoScott 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.
- jhallenworld 2y agoYuck, 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.
- j_timberlake 2y agoThe 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".
- jchw 2y agoStuff 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.
- consp 2y ago> 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.
- jchw 2y agoMakes 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=Pilots%20and%20flight%20crew%20receive,International%20Commission%20on%20Radiological%20Protection. https://pmc.ncbi.nlm.nih.gov/articles/PMC9447865/#:~:text=Pi...
- eqvinox 2y agoIf 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.
- natmaka 2y agoIs the load factor of those Japanese machines similar to those used in the US? Isn't life expectancy multifactorial?
- eqvinox 2y agoThe 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…
- lokar 2y agoStatistical 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?
- justlikereddit 2y agoRadiation 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.
- drpgq 2y agoWould you be able to see this effect comparing Americans and Canadians, assuming Canadians have way fewer CT scans on average?
- sagolikasoppor 2y agoI 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.
- tempera 2y agoExperts did not yet found that the mRNA Spike Vax causes cancer.
- doesnotexist 2y agoThis 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-s1-60488/ct-scan-cancer-risk-ionizing-radiation http://npr.org/sections/shots-health-news/2025/04/16/g-s1-60...
- grakasja 2y agoProtip: 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.
- 1970-01-01 2y ago5% 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 https://en.wikipedia.org/wiki/Replication_crisis