DICOM PS3.3 2024a - Information Object Definitions
C.8.8.14.6 Absolute and Relative Machine Coordinates

All treatment machine parameters except couch translations are specified in absolute machine coordinates as defined by [IEC 61217]. For the Table Top Vertical Position (300A,0128), Table Top Longitudinal Position (300A,0129), and Table Top Lateral Position (300A,012A), if the first Control Point contains a value of non-zero length, all subsequent Control Point position values are absolute values in their respective coordinate system. If the first Control Point contains a zero-length value, all subsequent Control Point position values are specified relative to the (unknown) initial value.

DICOM PS3.3 2024a - Information Object Definitions