Can anyone (with a better understanding of radiation risks) confirm the math for the added mortality risk from a single CT? I know a CT is a lot of radiation, but the mortality risk seems very high.
> Maybe. Kind of. Our knowledge of how radiation causes cancer comes primarily from Hiroshima and Nagasaki; we can follow survivors who were one mile, two miles, etc, from the center of the blast, calculate how much radiation exposure they sustained, and see how much cancer they got years later. But by the time we’re dealing with CAT scan levels of radiation, cancer levels are so close to background that it’s hard to adjust for possible confounders. So the first scientists to study the problem just drew a line through their high-radiation data points and extended it to the low radiation levels - ie if 1 Sievert caused one thousand extra cancers, probably 1 milli-Sievert would cause one extra cancer. This is called the Linear Dose No Threshold (LDNT) model, and has become a subject of intense and acrimonious debate. Some people think that at some very small dose, radiation stops being bad for you at all. Other people think maybe at low enough doses radiation is good for you - see this claim that the atomic bomb “elongated lifespan” in survivors far enough away from the blast. If this were true, CTs probably wouldn’t increase cancer risk at all. I didn’t consider myself knowledgeable enough to take a firm position, and I noticed eminent scientists on both sides, so I am using the more cautious estimate here.
The conventional approach for radiation protection is based on the ICRP's linear, no threshold (LNT) model of radiation carcinogenesis, which implies that ionizing radiation is always harmful, no matter how small the dose. But a different approach can be derived from the observed health effects of the serendipitous contamination of 1700 apartments in Taiwan with cobalt-60 (T1/2 = 5.3 y). This experience indicates that chronic exposure of the whole body to low-dose-rate radiation, even accumulated to a high annual dose, may be beneficial to human health.
... though some evidence against it with leukemia it seems, but this is not my field.
The non linearity intuitively makes sense. If I (naively) assume that DNA has some built in correcting codes (iirc it at least has some redundancy), one would be able to damage it up until the error rate that can be corrected without any deleterious effect.
I thought of this too, but then it also seems like too simple a mistake for someone like Scott Alexander to make in public, so I thought I must be misunderstanding his argument.
