DICOM PS3.3 2024b - Information Object Definitions
C.8.8.5.4 SOP Class UID in RT Referenced Study Sequence

Since RT Referenced Study Sequence (3006,0012) is Type 3, the Attribute may be omitted.

If RT Referenced Study Sequence (3006,0012) is present with an Item, for each Item, the SOP Class UID is that of the Study itself, not of the Instances within the Study. The Detached Study Management SOP Class (Retired) ("1.2.840.10008.3.1.2.3.1") may be used in Referenced SOP Class UID (0008,1150) in lieu of there being any other private or standard Study SOP Class defined.

Note

The SOP Class of an Instance (e.g., of one of the images within the referenced Study) is not used, even if all of the Instances within the Study are of the same Instance SOP Class.

DICOM PS3.3 2024b - Information Object Definitions