Accident Accounts

Donna Gartner: July 26,1985

The Therac-25 operator activated the machine, but after 5 seconds, the Therac-25 shut down and showed an "H-tilt" error message. The computer screen indicated that no dose had been given, so the operator hit the "P" key for the "proceed" command. The Therac shut down in the same manner as before, reading "no dose," so the operator repeated the process a total of four times after the initial try.

After the fifth try, a hospital service technician was called but found no problems with the machine. Donna Gartner left the clinic and the Therac was used with six other patients that day without any incidents. However, despite the fact that the Therac had indicated that no radiation dose had been given during Donna Gartner's five therapy attempts that day, Gartner complained of a burning sensation she described as an "electric tingling shock" in the treated area of her hip.

Gartner returned for treatment three days later, on July 29, and was hospitalized for suspected radiation overexposure. She had considerable burning, pain and swelling in the treatment region of her hip.
The Hamilton clinic took the Therac-25 machine out of service and informed AECL of the incident. This was the first time AECL had heard from a clinic about an overdose problem with the Therac-25 machine. AECL sent a service engineer to investigate.

AECL reported to a range of stakeholders that there was a problem with the operation of Therac 25. The FDA, the Canadian Radiation Protection Board (the parallel Canadian agency to the FDA), and other Therac-25 users were all notified. Users were instructed to visually confirm that the Therac turntable was in the correct position for each use.

Because of the Hamilton accident, AECL issued a voluntary recall of the Therac-25 machines and the FDA audited AECL's modifications to the Therac. AECL could not reproduce the malfunction that had occurred but suspected some hardware errors in a switch that monitored the turntable position. A failure of this switch could result in the turntable being incorrectly positioned, and an unmodified electron beam striking the patient. The company redesigned the mechanism used to lock the turntable into place, redesigned the switch to detect position and it accompanying software. They then reported in November 1985 that this redesign was complete and that, given their safety analyses, the machine was now at least 10,000 times safer than before.

Donna Gartner died on November 3, 1985 from cancer. An autopsy revealed that had the cancer not killed Gartner, a total hip replacement would have been necessary because of the radiation overexposure.