Hi Alex,
The answer to this depends on what you want to do with the RTSTRUCT. If you just want to store it in XNAT along side the other series in a study, there isn't really anything special to do, as the normal upload mechanisms will handle it just fine as long as the based series are also uploaded with the RTSTRUCT. If you're trying to view the RTSTRUCT in the OHIF Viewer Plugin, you'd need to get it into an "ROI Collection" [container for the RTSTRUCT within XNAT] assessor that the viewer expects. I think your options for that are...
Thanks,
Charlie