Simply lack of paying attention to details.In a majority of the recent cases of incompetence, radiotherapy throughout the country, the question has to do with who validates the treatment planning, and the answer is, it's supposed to be the medical physicist. In some cases it's not a matter of over-dosing the patient, it's also under-dosing the patient. The root cause isn't simply making the equipment better. Doctors plan treatment, medical physicists setup the treatment plan and it's absurd that there is minimal verification.
One answer is to have real-time patient dosimetry and someone actually watching the procedure. If there is any reason a dose is incorrect, the technologists needs to turn the unit off.
It's pathetic that a majority of physicians simply don't know enough about, or care, about radiation and radiation safety. The large lobbyist groups, such as AMA, don't help!