Rotating source descriptions can be simplified for many irradiations. For sources rotating in a plane (such as for CT and CBCT acquisitions), the encoding of a single transformation matrix for the position and orientation of the X-Ray Source RCS relative to the RDSR RCS, along with the center of rotation, a normal vector for the plane of rotation, and rotation angles at different points in time, is sufficient to calculate subsequent positions and transformation matrices.

This is encoded in TID 10050 “X-Ray Source Reference Coordinate System”. Figure UUUU.4.1.1.1-1 illustrates the X-Ray Source rotating in a plane.