Notice doctor adopting new approach (6)
I believe the answer is:
advent
'approach' is the definition.
(I've seen this before)
'notice doctor adopting new' is the wordplay.
'notice' becomes 'ad'.
'doctor' becomes 'vet' (vet is a kind of doctor**).
'adopting' indicates putting letters inside.
'new' becomes 'n'.
'vet' going around 'n' is 'vent'.
'ad'+'vent'='ADVENT'
(Other definitions for advent that I've seen before include "Christian season" , "Run-up to Christmas" , "appearance" , "introduction" , "Pre-Christmas period" .)