I'm writing a program to analyse radiotherapy treatment plans exported
in Dicom-RT. I'm having trouble understanding the RT DVH Module tags
(3004,0001) DVH Type and (3004,0054) DVH Volume Units.

Regarding DVH Type, I have seen exports from two different treatment
planning systems both of which have DVH type of CUMULATIVE, but one has
a constant bin width (eg. 0.1, 0.1, 0.1...) whereas the other has an
incrementing bin width (eg. 10, 20, 30, 40...). Is there another tag I
need to take into consideration to reconcile these two situations?

Regarding DVH Volume Units, when the value is PERCENT, is there any
information regarding total volume, ie, percent of what?

Any advice or pointers to relevant parts of the docs would be much