It makes more sense to be in a patient gown rather than brand new gym clothes after Doc Mitchell rescues the player character. Overall it is silly. After the player gets the Vault suit, the patient gown is returned to Doc Mitchell.
The concept is described in below mod. However the mod itself is incompatible with TTW because of the quest alterations.
http://www.nexusmods.com/newvegas/mods/44143/?