There is better way to do this?
I don't think so - that is the way the DICOM standard has structured that information.
You can shorten the line by using intermediate variables if you wish, e.g.
refd_FoR = myrt.ReferencedFrameOfReferenceSequence[0]
refd_study = refd_FoR.RTReferencedStudySequence[0]
and so on.