Editing Scanco Administration (section)

===XtremeCT II radiation dose===

In late 2023, Laura Cerbone visited the lab and did a series of X-ray dose calculations with equipment provided by Errol Stewart at AHS. She wrote a full report titled REPORT Dose assessment on the XtremeCT II (9Jan2024).pdf

For the knee protocol we have 936 mAs (for the 6 stacks), meaning 156 mAs for a single 168 slices stack.
For the tibia protocol we have 71 mAs.
Rescaling the DLP or the CTDI we measured for the tibia we would have:
 
 DLP(knee) = (156/71)*1.04 = 2.28 mGy
 CTDI(knee) = (156/71)*10.2 = 22.40 mGy

As for the k factors, there is no k-factor for the knee in that table, but Laura found a paper (“Estimates of Effective Dose for CT Scans of the Lower Extremities”, DOI: 10.1148/radiol.14132903) 
where they computed the k-factor for lower extremities for a spiral CT. The kV and the current used for this study are slightly different (e.g., we have a cone beam CT, not a spiral).
Nevertheless, using their k-factor to convert the DLP(tibia) to the effective dose we got 2µSv (lower but of the same magnitude as the one declared by Scanco). In principle, one could 
use the factor they found in this paper (0.0004 mSv/(mGy*cm)) for the knee, which would yield an effective dose of around 10 uSv (for a scan length of 10.2 mm, otherwise 60 uSv for the whole knee exam). 

The effective dose is computed by multiplying the DLP by the k-factor or, equivalently, multiplying the CTDI_vol (equivalent to weighted for us because we have a cone beam CT) by the scan length and the k-factor.
In our case we have
 
TIBIA:
 ED = DLP * k-factor = CTDI_vol * scan length * k-factor = 10.16 mGy * 1.02 cm * 0.0002 mSv mGy^-1 cm^-1 = 2.07 x 10^-3 mSv = 2.07 microSv
 
KNEE:
 ED = DLP * k-factor = CTDI_vol * scan length * k-factor = 22.4 mGy * 6.12 cm * 0.0004 mSv mGy^-1 cm^-1 = 0.0548 mSv = 54.8 microSv
 
Now, this calculation is not precise and it relies on factors that were computed for a different type of exam. In addition, we don’t know how they compute the effective dose at Scanco.

Stefan Hämmerle wrote on January 16, 2024:

 We go with the [https://www.icrp.org/publication.asp?id=ICRP%20Publication%20103 ICRP Publication 103] where to my knowledge the definition of effective dose comes. There you have different weighting factors for different organs and you have to take into account if an organ is only partly irradiated. For e.g. total skin surface and bone surface and so on we use some estimation from other ICRP Publications and can estimate with that the fraction of these organs we irradiate with the primary beam. Additionally we add something for the stray radiation and for the scout view. With that we end up to something below 3µSv, which we rounded up to below 5µSv to be on the safe side. 


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