Ketone prefix organic chemistry nomenclature
The prefix ‘keto’ doesn’t exist in the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book). Already in the 1979 Recommendations, the prefix ‘oxo’ is used to indicate $\ce{=O}$ when the group cannot be cited as suffix.

Nevertheless, the Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995) still remembers the use of the prefix ‘keto’:


  To indicate a double-bonded oxygen that is part of a ketonic structure, the term keto is sometimes used as a prefix, but such use has been abandoned by IUPAC for naming specific compounds. A traditional use of keto is for indicating oxidation of $\ce{CHOH}$ to $\ce{C=O}$ in a parent compound that contains $\ce{OH}$ groups, such as carbohydrates. E.g. 3-ketoglucose.