5 ms·

>If you do the math by ICRP formulae, you end up with increase chance of cancer of 1 in 2600 over the next 20 years from a single 7ms CT scan today. This compar

>If you do the math by ICRP formulae, you end up with increase chance of cancer of 1 in 2600 over the next 20 years from a single 7ms CT scan today. This compares favorably with "natural" risk that is 1 in 10 without any extra exposure above background radiation. But that is a meaningless comparison. The doctor should be comparing this additional risk, to the benefit of the scan. The "natural" risk of developing cancer is totally irrelevant to the cost-benefit analysis.

carbocation 13y ago
Because we operate in likelihood ratios, the unexposed risk is important so the risk can be computed (at least, in theory; in practice, people go more by indication than by formal risk prob/benefit prob).
- yetanotherphd 13y ago
  That still makes no sense. If I want to know whether to do a CT scan, the only relevant fact is the increase in probability (in an absolute sense) of cancer that it causes. It seems like either you, or the entire field of medicine, is obfuscating this basic fact using some field-specific concepts. EDIT: It seems like you are referring to relative risk (http://en.wikipedia.org/wiki/Relative_risk http://en.wikipedia.org/wiki/Relative_risk). But as I said, there is no reason that relative risk should be considered in this case.
DenisM 13y ago
I see your point. I wonder though if there should be a cutoff somewhere, below which you stop caring? I used background cancer rates as an anchor to judge if the cutoff has been reached, without getting specific about benefits of treatment in each particular case. Would you suggest another cutoff level that is broadly applicable?
- yetanotherphd 13y ago
  I think the only comparison that makes sense is the benefit from the scan. So if you are certain that the benefit of the scan is, no matter what the particular case, going to be worth much more than a 1/1000 chance of getting cancer, then that is a reason to ignore the risk.

carbocation 13y ago

Because we operate in likelihood ratios, the unexposed risk is important so the risk can be computed (at least, in theory; in practice, people go more by indication than by formal risk prob/benefit prob).

yetanotherphd 13y ago
That still makes no sense. If I want to know whether to do a CT scan, the only relevant fact is the increase in probability (in an absolute sense) of cancer that it causes. It seems like either you, or the entire field of medicine, is obfuscating this basic fact using some field-specific concepts. EDIT: It seems like you are referring to relative risk (http://en.wikipedia.org/wiki/Relative_risk http://en.wikipedia.org/wiki/Relative_risk). But as I said, there is no reason that relative risk should be considered in this case.

DenisM 13y ago

I see your point. I wonder though if there should be a cutoff somewhere, below which you stop caring? I used background cancer rates as an anchor to judge if the cutoff has been reached, without getting specific about benefits of treatment in each particular case. Would you suggest another cutoff level that is broadly applicable?

yetanotherphd 13y ago
I think the only comparison that makes sense is the benefit from the scan. So if you are certain that the benefit of the scan is, no matter what the particular case, going to be worth much more than a 1/1000 chance of getting cancer, then that is a reason to ignore the risk.