In the retrospective epidemiological study of CT exposure there is a need to calculate individual organ absorbed dose for each cohort member to assess the cancerogenic excess risk. The problem is the loss of some key parameters which are necessary: patient's size, kV, tube current and others.
If you have DICOM images, values of kVs and mAs should be listed in every slice of the CT (check DICOM viewer of the header). Effective dose per organ can be estimated from this values, using organ-specific sensitivities of the organ. If you know what type of CT scanner was used for this patient, you can calculated the dose with the ImPACT dosimetry calculation software, or use one of the methods listed in the AAPM report of the EFOMP:
https://www.aapm.org/pubs/reports/RPT_246.pdf
Dear Colleagues, thank you for sharing this report!
I think, the main problem for this kind of retrospective study is lack of info, such as DICOM headers, in the early years of CT implementation (no digital data stored).
You might considere to build a look up table, with value of organ dose by time period and age range. You first collect typical parameter used in certain time period and age range and then you calculate the dose for each age and time period.
This approach is of course coming with uncertainty but has been used in such type of retrospective study (i.e Preston-Martin S 2003).
See this publication that describe how to get such type of look up table >>>> Trends in Estimated Thyroid, Salivary Gland, Brain, and Eye Lens Doses From Intraoral Dental Radiography Over Seven Decades (1940 TO 2009) (Health Physics)
See this abstract (full publication accepted, coming soon) for the above mention exposure assesment approach in an epidemiological study >>>>
Brain tumor risk after exposure to medical ionizing radiation: results from the MOBI-kids study
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