Earlier quoted context omitted.
"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.…
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/
Develop cancer, or die of cancer? Alexander seems to be claiming the latter.