The Isocenter coordinate system (O,X,Y,Z) of the equipment is defined as follows:

The Positioner Coordinate System (O_p, X_p, Y_p, Z_p) is defined as follows:

The Positioner Coordinate System (O_p, X_p, Y_p, Z_p) is characterized, with respect to the Isocenter Coordinate System (O, X, Y, Z), by two angles describing the X-Ray center beam, and a third angle describing the rotation of the X-Ray detector plane. These angles are relative to the Isocenter reference system, and independent from the patient position on the equipment.

Positioner Isocenter Primary Angle (0018,9463) (so-called Ap₁ in Figure C.8.19.6-6) is defined in the plane XY, as the angle between the plane YZ and the plane Y_pZ. The axis of rotation of this angle is the Z axis. Angle from -Y to +X is positive. The valid range of this angle is -180 to +180 degrees.

Positioner Isocenter Secondary Angle (0018,9464) (so-called Ap₂ in Figure C.8.19.6-6) is defined in the plane Y_pZ, as the angle of the X-Ray Center Beam (i.e., Y_p) relative to the XY plane. The axis of rotation of this angle is perpendicular to the plane Y_pZ. Angle from the plane XY to +Z is positive. The valid range of this angle is -180 to +180 degrees.

Positioner Isocenter Detector Rotation Angle (0018,9465) (so-called Ap₃ in Figure C.8.19.6-6 and in Figure C.8.19.6-7) is defined in the detector plane, as the angle of the vertical scan-lines of the detector (i.e., Z_p) relative to the intersection between the detector plane and the plane Y_pZ. The sign of this angle is positive clockwise when facing on to the detector plane (see Figure C.8.19.6-7). The valid range of this angle is -180 to +180 degrees.

The table coordinate system (O_t, X_t, Y_t, Z_t) is defined as follows:

- Origin O_t, so-called Table Reference Point, is on the Table Top plane

- +X_t direction to the TABLE LEFT

- +Z_t direction to the TABLE HEAD

- +Y_t direction to the TABLE DOWN

The table coordinate system (O_t, X_t, Y_t, Z_t) is characterized, with respect to the Isocenter coordinate system (O, X, Y, Z), by a 3D translation and 3 angles describing the tilting and rotation:

Table X Position to Isocenter (0018,9466) (so-called T_X in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O_t with respect to the Isocenter Coordinate System in the X direction. Table motion toward +X is positive.

Table Y Position to Isocenter (0018,9467) (so-called T_Y in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O_t with respect to the Isocenter Coordinate System in the Y direction. Table motion toward +Y is positive.

Table Z Position to Isocenter (0018,9468) (so-called T_Z in Figure C.8.19.6-8) is defined as the translation of the Table Reference Point O_t with respect to the Isocenter Coordinate System in the Z direction. Table motion toward +Z is positive.

Table Horizontal Rotation Angle (so-called At₁ in Figure C.8.19.6-9) is defined in the horizontal plane XZ, as the angle of the projection of the +Zt axis in the XZ plane relative to the +Z axis. The axis of rotation of this angle is the vertical axis crossing the Table Reference Point Ot. Zero value is defined when the projection of +Zt in the XZ plane is equal to +Z. Angle from +Z to +X is positive. The valid range of this angle is -180 to +180 degrees.

Table Head Tilt Angle (so-called At₂ in Figure C.8.19.6-9) is defined in the vertical plane containing Z_t (i.e., YZ_t), as the angle of the +Z_t axis relative to the horizontal plane XZ. The axis of rotation of this angle is defined as the intersection between the horizontal plane XZ and the plane X_tY_t. Zero value is defined when +Z_t is contained in the horizontal plane XZ. Angle from horizontal (plane XZ) to -Y direction (upwards) is positive, indicating that the head of the table is above the horizontal plane. The valid range of this angle is -45 to +45 degrees.

Table Cradle Tilt Angle (so-called At₃ in Figure C.8.19.6-9) is defined in the X_tY_t plane, as the angle of the +X_t axis relative to the intersection between the X_tY_t plane and the horizontal plane XZ. The axis of rotation of this angle is the axis Z_t. Zero value is defined when +X_t is contained in the horizontal plane XZ. Angle from horizontal (plane XZ) to -Y direction (upwards) is positive, indicating that the left of the table is above the horizontal plane. The valid range of this angle is -45 to +45 degrees.