CT scans could cause 5% of cancers, study finds; experts note uncertainty

Posted by pseudolus 4/15/2025

CT scans could cause 5% of cancers, study finds; experts note uncertainty(arstechnica.com)

130 points | 153 commentspage 2

jchw 4/15/2025|

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.

consp 4/15/2025|

> 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 4/15/2025||

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...

1970-01-01 4/17/2025||

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

tgv 4/15/2025||

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?

itishappy 4/15/2025||

It's quite hard to give bones and joints cancer. Cancer prefers dividing cells.

ahartmetz 4/15/2025||

Some blood cells are produced in bone marrow and it's not rare to get "bone cancer".

itishappy 4/15/2025||

Yup, but it's significantly less common than most other forms of cancer.

ceejayoz 4/15/2025||

If cancer is also rare in those spots without a CT, that would seem to indicate a major confounding variable at play.

tgv 4/15/2025||

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.

ceejayoz 4/15/2025||

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.

tgv 4/16/2025||

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.

sakex 4/15/2025||

What about MRI? Just had one. Sorry if it's a stupid question, I don't know much about this

hylaride 4/15/2025||

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.

ashleyn 4/15/2025|||

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.

tgv 4/15/2025|||

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.

bluGill 4/15/2025|||

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.

rasmus1610 4/15/2025|||

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.

bluGill 4/15/2025||

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.

mthomasmw 4/15/2025|||

citation?

petters 4/15/2025||

You're safe

Zezima 4/15/2025||

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...

ceejayoz 4/15/2025||

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/.

el_benhameen 4/15/2025|||

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.

blitzar 4/15/2025|||

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.

sph 4/15/2025||

I don’t think they roam among us “plebs”

blitzar 4/15/2025||

With the advent of these modern medical breakthroughs I believe we have been rebranded from "plebs" to "blood bags".

AyyEye 4/15/2025|||

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.

queuebert 4/15/2025||

If it's any consolation, a sinus CT is tuned to have a very low radiation dose compared to typical body CT scans.

queuebert 4/15/2025|||

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.

stevenwoo 4/15/2025|||

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.

chr1 4/15/2025|||

In most cases instead of CT scan one could do the same diagnosis with MRI scan, which is only a bit more expensive.

ChocolateGod 4/15/2025||

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.

miiiiiike 4/15/2025|||

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.

fatnoah 4/15/2025||

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.

miiiiiike 4/16/2025||

I don't like this coin. Sorry about your dad.

fatnoah 4/16/2025||

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.

miiiiiike 4/17/2025||

Yeah, I got your meaning. Very well put.

cowfarts 4/15/2025||

[dead]

grakasja 4/16/2025||

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.

doesnotexist 4/16/2025||

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...

sagolikasoppor 4/16/2025||

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.

canadiantim 4/15/2025||

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

justlikereddit 4/15/2025|

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.

drpgq 4/16/2025|

Would you be able to see this effect comparing Americans and Canadians, assuming Canadians have way fewer CT scans on average?

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