One scans radius on, say, monthly attendant in centre for patients (6)

I believe the answer is:

imager

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'monthly attendant in centre for patients' is the definition.
I can't tell whether this defines the answer.

'one scans radius on' is the wordplay.
'one' becomes 'i' (roman numeral).
'scans' becomes 'mage' (I can't explain this - if you can you should believe this answer much more).
'radius' becomes 'r' (abbreviation in geometry).
'on' is a charade indicator (letters next to each other).
'i'+'mage'+'r'='IMAGER'

'say' is the link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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