[abainbridge]

The paper he links to [1] broadly agrees with his statement, eg "An estimated 1 in 270 women who underwent a coronary angiography CT at age 40 will develop cancer from that CT (1 in 600 men), compared with an estimated 1 in 8,100 women who had routine head CT at the same age (1 in 11, 080 men)".

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/

[sgt101]

I felt less compelled by the paper after reading " 1,119 " as the sample size - how the fin f they think that they can get to estimates like 1:11,080 with a sample size of 1,119 I do not know.

Going the other way: on the internets I read that there are 5 million CT scans in the UK every year. If there was a 1:10k rate of cancer from these we would see 500 fatal cancers a year. If there was a 1:600 risk then we would see 8300 cancers a year. There are 400k cases of cancer per year in the UK as it is. So, at the top end about 2% of cancer could be hypothesized as from CT scans based on these numbers however they were extracted kicking and screaming from the case notes.

There is an interesting twist on this though - the mortality of people who get CT scans is probably much higher than the mortality of people who don't as there is probably a reason why they are getting the scan. One reason I have seen for people to get a CT scan is that they have metastasizing cancer. If you have metastasizing cancer you are probably going to get radiotherapy. Now, radiotherapy doses are quite difficult to understand as there is a big difference in the way it gets absorbed and handled, but as a layperson I look at the numbers and think that radiotherapy doses seem much bigger than CT scan doses. But I don't even know how I would go about comparing them and controlling for them in the stats.

I personally would have to sit and think for a long time about how to sort the causal factors out in the stats around this, I think I would not be doing that on a sample of 1k people.

[JeremyNT]

> The paper he links to [1] broadly agrees with his statement, eg "An estimated 1 in 270 women who underwent a coronary angiography CT at age 40 will develop cancer from that CT (1 in 600 men), compared with an estimated 1 in 8,100 women who had routine head CT at the same age (1 in 11, 080 men)".

Develop cancer, or die of cancer? Alexander seems to be claiming the latter.

[abainbridge]

The thing I don't understand is that if the CT scan is more dangerous than having a kidney removed, then surely they'd take the kidney out to see if it was compatible with the recipient rather than give you such a dangerous scan.

[eru]

The kidney surgery only looks so low risk (partially) because they only do it on people that passed the CT scan.

(To give an even more extreme example for illustration:

Suppose the scan could perfectly predict who will die from the surgery and who will live without any side effects. Suppose 90% of people fall into the former and 10% of people fall into the latter category. Suppose further that the scan has a 0.1% chance of killing you.

If you scan people beforehand, it will look like the surgery has 0% chance of complications against 0.1% of the scan. But if you dropped the scan, all of a sudden the surgery would have a 90% death rate.)

[Taniwha]

One of the reasons they do the scan is that they look at both kidneys only take your WORST one

[Vecr]

If that's the case, is it possible Scott is lying or leaving out information on what kidney it was?

[TeMPOraL]

I'm guessing that <CT scan> is more dangerous than <having a kidney removed, given you've cleared the CT scan and other tests>. Plus, <having a kidney removed, studied, and then reinserted after failing some tests>, might be more dangerous than either.