DICOM PS3.3 2019b - Information Object Definitions
C.8.8.14.13 Angular Values in RT Beams Module

The Attributes that define angles refer to coordinate systems defined by IEC 61217. Where indicated in the DICOM Attribute definition, the angle uses the coordinate system (orientation of the rotation axis and the origin of the rotating coordinate system) defined in IEC 61217, however DICOM makes no restrictions on the range of values stored. IEC 61217 defines restrictions that only apply to user interface presentation.

DICOM PS3.3 2019b - Information Object Definitions