Object Selection Documents can be thought of as Structured Reports without the report!
Every DICOM Association starts with a process of negotiation whereby the Application Entities involved exchange sufficient information about themselves to allow proper communication.
This is a Normalised Instance which represents the state of a procedure step, and is:
A Presentation Context may be considered as a negotiated “sub-channel” with a DICOM Association through which the Application Entities have agreed to exchange information.
Radiotherapy objects were DICOM’s first foray into non-image Composite Instances - i.
In the vast majority of Associations, the Association is initiated by the SCU with the SCP responding, but DICOM does allow Reverse Role Negotiation whereby the initiator can request to be regarded as the SCP.