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I read somewhere that the average CTDIvol in CT scans at hospitals is ~40 mGy. This translates to the 'radiation intensity' at the center of the person, and can also be roughly interpreted as an 'absorbed or equivalent dose', but this is not the organ specific absorbed dose.

From medical literature, particularly the life span studies of RERF, I read that at 2500 meters the 'absorbed colon dose' was about 5 mGy [1].

Out of curiosity, I tried to figure out at what distance you would have to be from the epicenter of Hiroshima, to get the same level of 'absorbed colon dose' as the average CT Scan.

To convert, the ~40 mGy to 'absorbed colon dose', you use a tissue weighting factor [2]. The tissue weighting factor for the colon is 0.12. So, this means, the average CT Scan results in an 'absorbed colon dose' of ~40 mGy * 0.12 = ~4.8 mGy.

I realize there is a different concept of 'effective dose' that calculates risk of cancer based on organ type and organ weight scanned. That is not of interest for my calculations.

As far as purely 'absorbed dose' of the organs is concerned, is it accurate to say that the the average CT scan has the same effect on a person's organs as it would to someone standing just outside 2500 meters from the epicenter of Hiroshima?

[1] http://www.rerf.jp/general/qa_e/qa2.html
[2] https://www.euronuclear.org/info/encyclopedia/t/tissue-weight-factor.htm

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  • $\begingroup$ Good question, maybe one for the Physics Stack Exchange site? If I was standing 2.5km from the epicenter of Hiroshima the effect it would have had on my organs (especially my colon) would probably result in them emptying themselves. CT scan doesn't seem to do that... Usually. :) $\endgroup$ – Lyall Oct 27 '15 at 17:35

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