4 ms·

"the risk of dying from the screening exam was 1/660" For someone as smart as Scott Alexander, this is an astonishing mistake. If CTs were such death machines

"the risk of dying from the screening exam was 1/660" For someone as smart as Scott Alexander, this is an astonishing mistake. If CTs were such death machines, we would have seen a worldwide epidemics of CT-related cancers. There is no way you can cover up such a strong signal, given that people are screened all the time. Edit: thanks for unleashing such an interesting debate. I guess the problem is in my perception. "Risk of dying from the exam" means lifetime risk, while my perception was "1 of 660 people who get the exam drops dead pretty soon afterwards".

snarkconjecture 3y ago
It would be astonishing if it were a mistake. And yes, it's a detectable signal. "in a large population-based cohort it was found that up to 4% of brain cancers were caused by CT scan radiation" --somewhere on Wikipedia CT scans vary in dosage. Wiki gives ~10 Sv for an abdominal CT; I don't know where Scott got 30, but maybe the kidney screening is multiple scans or otherwise higher dose. Or he was wrong by a factor of 3, which is not a factor of 100. CT scans aren't done frivolously, and the current rate of scans is hotly debated for exactly this reason. I'm a little surprised that kidney donation involves CT over MRI by default, but I'm not an expert.
- Spooky23 3y ago
  Abdominal stuff often involves CT scans that need to be done in phases. For brain stuff, some things require CT vs MRI. Another risk is the contrast dye that’s often used in these studies. If you’re dealing with cancer monitoring or something that requires monitoring, you can develop allergies and poor reactions to that as well.
- abainbridge 3y ago
  > I don't know where Scott got 30 The text where he says that is a clickable link! https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/
- TeMPOraL 3y ago
  > I don't know where Scott got 30, but maybe the kidney screening is multiple scans or otherwise higher dose. Scott called it "multiphase abdominal CT". Quick searching on-line suggests[0] that the "multiphase" here stands for doing 3-4 scans within a minute or two of each other, as the contrast agent diffuses through the organ, giving you multiple images that inform you about different parts of the target structure. > Wiki gives ~10 Sv for an abdominal CT; (...) Or he was wrong by a factor of 3 If what I wrote above is correct, then it tracks - ~10 mSv for one CT, multiplied by 3-4 scans done in a multiphase CT, gives you ~30-40 mSv, which matches the number Scott posted. -- [0] - https://www.barnardhealth.us/dynamic-contrast/multiphasic-imaging-techniques.html https://www.barnardhealth.us/dynamic-contrast/multiphasic-im... - First link I found; CTRL+F "multiphase", as the relevant information is spread throughout the comments section.
- jmcgough 3y ago
  > CT scans aren't done frivolously As someone who works in the ED, we pretty much give CTs out like candy to avoid a lawsuit if we miss something.
  - snarkconjecture 3y ago
    I stand corrected.
abainbridge 3y ago
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/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/
- abainbridge 3y ago
  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.
  - TeMPOraL 3y ago
    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.
  - eru 3y ago
    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 3y ago
      One of the reasons they do the scan is that they look at both kidneys only take your WORST one

snarkconjecture 3y ago

It would be astonishing if it were a mistake. And yes, it's a detectable signal. "in a large population-based cohort it was found that up to 4% of brain cancers were caused by CT scan radiation" --somewhere on Wikipedia CT scans vary in dosage. Wiki gives ~10 Sv for an abdominal CT; I don't know where Scott got 30, but maybe the kidney screening is multiple scans or otherwise higher dose. Or he was wrong by a factor of 3, which is not a factor of 100. CT scans aren't done frivolously, and the current rate of scans is hotly debated for exactly this reason. I'm a little surprised that kidney donation involves CT over MRI by default, but I'm not an expert.

Spooky23 3y ago
Abdominal stuff often involves CT scans that need to be done in phases. For brain stuff, some things require CT vs MRI. Another risk is the contrast dye that’s often used in these studies. If you’re dealing with cancer monitoring or something that requires monitoring, you can develop allergies and poor reactions to that as well.
abainbridge 3y ago
> I don't know where Scott got 30 The text where he says that is a clickable link! https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4635397/
TeMPOraL 3y ago
> I don't know where Scott got 30, but maybe the kidney screening is multiple scans or otherwise higher dose. Scott called it "multiphase abdominal CT". Quick searching on-line suggests[0] that the "multiphase" here stands for doing 3-4 scans within a minute or two of each other, as the contrast agent diffuses through the organ, giving you multiple images that inform you about different parts of the target structure. > Wiki gives ~10 Sv for an abdominal CT; (...) Or he was wrong by a factor of 3 If what I wrote above is correct, then it tracks - ~10 mSv for one CT, multiplied by 3-4 scans done in a multiphase CT, gives you ~30-40 mSv, which matches the number Scott posted. -- [0] - https://www.barnardhealth.us/dynamic-contrast/multiphasic-imaging-techniques.html https://www.barnardhealth.us/dynamic-contrast/multiphasic-im... - First link I found; CTRL+F "multiphase", as the relevant information is spread throughout the comments section.
jmcgough 3y ago
> CT scans aren't done frivolously As someone who works in the ED, we pretty much give CTs out like candy to avoid a lawsuit if we miss something.
- snarkconjecture 3y ago
  I stand corrected.

abainbridge 3y ago

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

abainbridge 3y ago
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.
- TeMPOraL 3y ago
  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.
- eru 3y ago
  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 3y ago
    One of the reasons they do the scan is that they look at both kidneys only take your WORST one