RT Ion Plan contains an attribute Patient Support Type (300A,0350), which can be CHAIR or TABLE. The patient support type CHAIR does not change the coordinate axes of the patient support coordinate systems relative to their parent systems. It is more an attribute of the type like the patient position in imaging (i.e. HFS, HFP, …).
The orientation of the treatment chair shall be defined with the chair positioned in such way, that the patient looks towards the gantry bearing (or along the Y axis of the IEC FIXED system) if all angles, especially IEC PATIENT SUPPORT angle are 0(. All other parameters follow straight forward, once this definition is accepted. I.e. chair rotation is a rotation of IEC PATIENT SUPPORT coordinate system; a backward tilt of the chair is a positive rotation of the PITCHED TABLE TOP coordinate system. A translation of the chair is a translation of the IEC TABLE TOP system.
The roll angle is typically 0º.
For a seated treatment on a horizontal beam-line, the following angles are therefore defined:If IEC GANTRY angle is 90º (270º), IEC PATIENT SUPPORT angle is 270º (90º) for the position where the patient looks into the beam port.