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?

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.

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.

I went to the doctor complaining of constipation. He sent me for a CT scan which proved 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 in the CT scan session?

I really don’t buy it if someone says the opposite.

If the hallucination machine can cite a source, check and cite that for facts, but don't cite the hallucination machine.

What about contrast? I've heard it's really hard on your thyroid.

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.

Sounds like the CT scan was a clear win then.

An abdominal CT found a goiter?

They did chest too, I don't know why.

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.

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.

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.

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. It's a lot like during COVID how the medical community lied to the public about the effectiveness of N95 masks. Your individual health will always be less important than the integrity of their system.

"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.

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.

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).

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.

People get weird when using math to calculate human lives.

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...

As they should. It’s not difficult to use questionable math to justify very awful things.

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?

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

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.

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.

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.

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.

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 "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.

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”

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.

Yeah, no. A doctor that I had a feeling wasn't paying too close of attention to what I was saying ordered a pelvic/abdominal CT with and without contrast, ~30-40 mSv. Nothing turned up on the report. When I went back he said "Nothing was 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. I didn't even know the difference between an MRI and CT at the time.

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.

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.

I’ve remodulated my phaser arrays and randomized the stochastic spectral frequencies ten times, but those Borg keep adapting!!1

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