Acknowledgement of item reviewed in Radio Times at first (7)
I believe the answer is:
receipt
'acknowledgement' is the definition.
(receipt is a kind of acknowledgement)
'item reviewed in radio times at first' is the wordplay.
'item' becomes 'piece' (piece is a kind of item).
'reviewed' says the letters should be written in reverse.
'in' indicates putting letters inside.
'at first' suggests taking the first letters.
The initial letters of 'radio times' is 'rt'.
'piece' back-to-front is 'eceip'.
'eceip' inserted into 'rt' is 'RECEIPT'.
'of' is the link.
(Other definitions for receipt that I've seen before include "Evidence of sale" , "voucher" , "Acceptance" , "old cook's directions" , "Record of payment" .)