De or het routinebehandeling?

The correct Dutch article is:

de routinebehandeling

Rule Words ending in -ing: almost always de. See the rule

How to use routinebehandeling

the routinebehandelingde routinebehandeling
this routinebehandelingdeze routinebehandeling
that routinebehandelingdie routinebehandeling
our routinebehandelingonze routinebehandeling
your routinebehandelingjouw routinebehandeling
every routinebehandelingelke routinebehandeling
which routinebehandeling?welke routinebehandeling?
a big routinebehandeling / the big routinebehandelingeen grote routinebehandeling, de grote routinebehandeling