Can one of my fellow staff (married and practicing muslim) act as my mahram when going for upgrading training abroad from my place of work, or should i refuse to join? I am a radiographer, i have been offered appointment in Radiotherapy and oncology department few months ago. Will actually need the training as part of what will make me qualify as Radiation therapist but can't find mahram that is less busy now.

You have to go with your mahram because a work mate does not qualify as one.