Pitch and Roll Coordinate Systems of the Table Top are defined in [IEC 61217]. These angles are defined as rotations of the IEC Table Top System as indicated below.

The Table Top Pitch Angle is defined as the rotation of the coordinate axes Yt, Zt about axis Xt by an angle ψt; see Figure C.8.8.14-1. An increase in the value of angle ψt corresponds to the clockwise rotation of the Table Top as viewed from the Table Top coordinate system origin along the positive Xt axis.

The Table Top Roll Angle is defined as the rotation of the coordinate axes Xt, Zt about axis Yt by an angle ψt; see Figure C.8.8.14-2. An increase in the value of angle ψt corresponds to the clockwise rotation of the Table Top as viewed from the Table Top coordinate system origin along the positive Yt axis.

It is important to observe that the point of rotation is the origin of the table top system after the rotation of the PATIENT SUPPORT(s) system about Zs by θs after the rotation of the Table top eccentric rotation (e) system about Ze by θe and after the translation of Table top (t) system along Xe Ye Ze. This means that the rotation point of the Pitch and Roll angles is typically not the isocenter. The translational values Xt Yt Zt may need to be adjusted to preserve the patient position at the isocenter. e.g., a rotation of the Pitch angle by a positive angle at a position originally at Xt=0, Yt=100 and Zt=0 will lead to a negative Zt value and a slightly lower Yt if the patient position at isocenter is to be maintained.

The Pitch Angle rotation is applied before the Roll Angle rotation.