Hi again
I think it is clever to use low vac-loc under the legs, since the more steep the knee angle is, the more AlignRT pitch can cheat you in the bony pelvis area with ROI that includes more legs. To me it seems that there can be even negative correlation in pitch between the 1) legs and the bony 2) symphysis and l5, of which 2) is typically the matching area of interest in the kV/kV images in the pelvis) , since those 1) and 2) do not necessarily move as a one rigid object. For that reason I see that if we include more ROI to the legs with the typical commercial knee/feet fixation device, we have to concentrate that the patient/knees are fixated daily properly on the couch, which may need also indexed fixation under head. These things may have influence on LNG errors we have found and pitch- related errors Victoria has found.
Marko