A therapist is going to take a port film on a patient, and s…

A therapist is going to take a port film on a patient, and selects port film at the treatment machine.  The therapist verifies all other parameters and presses the beam on button to take the port film.  The therapist suddenly realized that the treatment field was accidentally selected rather than the port film, and turns the beam off.  Which category of behavior does this mistake fall under?