Michael Tallhamer, MSC, DABR
Marko and Ellen,
I would add (or caution) that vertebra match should be scrutinized as a good indicator for BH as the heart position is a compound motion during the BH. The primary reason for BH is to protect the heart and you have to be careful in making adjustments for BH level based on vertebral match alone. We take kVs on the first day under BH for rough verification of isocenter location and BH level but our final verification is always a tangential port with the heart and heart block relative positions indicating the proper BH and positioning after kV verification.
We find that we rarely have to make any adjustments away from the BH DICOM surface when evaluated against the kVs and/or the MV ports showing the heart and heart block locations.