I don't think that there is a need for monitoring since radiotracer usually have a short halflife, they usually use fluoride-18 (half life 110min) to replace a

I don't think that there is a need for monitoring since radiotracer usually have a short halflife, they usually use fluoride-18 (half life 110min) to replace a -OH or a well placed -H in a molecule that bind to the site of interest (ex: glucose -> fluorodeoxyglucose, levodopa -> fluorodopa).