Actually, CTD is the usual abbreviation for Cyclophosphamide + Thalidomide + Dexamethasone, not CDT. (If you need convincing try Googling CTD myeloma, then try Googling CDT myeloma.)
It’s not obvious that it should be one or the other. I sometimes have to think twice when I use the abbreviation in speech. CTDa is the attenuated version that has a reduced dexamethasone dose, which can help you get it the right way round if you remember that the ‘a’ is associated with the ‘D’.
Vel/Dex and Vel-Dex are common abbreviations for Velade + Dexamethasone, but VD and Vd are also used. CVD, VCD and CyBorD are all used for Cyclophosphamide + Velcade (Bortezomib) + Dexamethasone.
I can remember thinking that the liberal peppering of abbreviations made some posts (and medical literature) quite difficult to follow when I started looking up about myeloma. It’s not helped by the variation in abbreviations for the same drug. Velcade, for example, can be V (as in CVD), Vel (as in Vel/Dex) and Bor (as in CyBorD) and possibly others. It would be nice to have the consistency of chemical symbols.