DICOM PS3.3 2021e - Information Object Definitions
A.34.17.4.5 Waveform Sample Interpretation

For channels encoding the patient's position as fixed values the value of Waveform Sample Interpretation (5400,1006) is UB.

For channels encoding the patient's position as rotation angles the value of Waveform Sample Interpretation (5400,1006) is SS.

DICOM PS3.3 2021e - Information Object Definitions