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Therac-25 Case
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How to Produce a Malfunction 54 on a [AECL] Therac-25
Linear Accelerator
This statement was written by the East Texas Cancer Center physicist after he discovered how to reproduce the Malfunction 54 error
Enter the room and set up the machine for an electron beam treatment by selecting a field size and installing the trimmers. Press the set button. Leave the room and close the door. At the control console proceed to the patient set-up display. For Mode enter "X". The machine will default to 25 MeV and go to dose rate of 250 rads/min. Use return key to go to dose. Enter 200. Use return key to go to time. Enter 0.8 min. Use the return key to rapidly advance to the bottom of the display. Immediately use the up arrow to move from the bottom of the display. You are now in the edit mode. Use the up arrow to go to the top of the display and change the mode "X" to "E" for electrons. Change the energy from 25 to 10. Use the return key to go back down to the bottom of the display. Wait for the "beam ready" message then type "B" return. The unit will have no indications on dose rate or dose 1 or dose 2 for about 3 to 4 seconds. Then the dose rate will flash 550 to 575 for one cycle and return to zero. Dose 1 and Dose 2 will count to -6. A malfunction 54 message will appear at the bottom of the display. You have just delivered a dose of approximately 25,000 rads of 25 MeV electrons in less than two seconds.