do not cut them.
the canes of all Dendrobium (and most orchids) are useful to the plant as a storage for food and water that the plant can draw upon when its usual supply is short and the plant needs more.
Additionally some dens like Nobile types flower best on the old bare canes. If you cut them you will have no flowers.
When the plant gets too many old canes you will quickly know as they will shrivel and dry up to where they can be pulled off with very little pressure.
This Dendrobium had 1000 flower buds on bare canes and none on young canes with leaves.
