Scaling for MV/kV phantoms

Is it possible to have a quick calculation of MV/kV scaling (as in TG-142) from a SI QC-3 and QC-kV1 phantom? I would like to use the setup SSD, calculated phantom ROI, and known phantom dimensions to get an estimate (e.g. say its 15cm x 10cm, and I get 15.1cm x 10.1cm, or a 1mm error in scaling). Similar to what is done on the CatPhan geometry line average.


It is. The main reason I hadn’t added it is because the scaling was usually just slightly off from the ideal, even when set up perfectly. At iso it should be pretty good but the finite thickness of the phantom creates a penumbra of sorts around the edges. When the phantom sits on the panel the phantom isn’t at the claimed SSD usually. E.g. if I set it on the panel and say SSD=1500, that’s the SID, but SSD is really a few cm away. It’s good enough to get the analysis but the absolute size of the phantom will be off a few percent. I guess if it’s claimed to simply be a constancy check then it could work. This would probably be easiest to use the area of the phantom. Small angle rotations cause left/right up/down lengths to differ above the tolerance. The size is only a scalar value and does not give x/y details, but I don’t know how it would be physically possible to have your EPID have bad scaling in one axis and correct in another.