The Therac-25 Radiation Therapy Machine

The Atomic Energy of Canada Limited (AECL) created the Therac-25 radiation therapy machine (Death and Denial). The major innovation of this machine is that it was much more computer-controlled than the previous machines of its kind. This enabled technicians to spend less time setting up the machine and more time working directly with patients. The reduced setup time also increased the number of patients that were able to be treated in one day (ComputingCases). Patients undergoing treatment from the Therac-25 are in communication with the machine operator (located in a separate room) through AV monitors (Death and Denial).

The software for the Therac-25 was an evolution from the two previous machines, the Therac-6 and the Therac-20. The development of the software was completed by only one programmer. The Therac-25 relied much more heavily on its software than the previous versions, which relied mostly on the operator. This machine also changed the way safety checks were performed; critical safety checks were included in the hardware and software of previous machines, but only software on the Therac-25 (Death and Denial, The Software).

The Therac-25 was released to market in 1983 and is still in use today (ComputingCases). “Between June 1985 and January 1987, six patients were seriously injured or killed by unsafe administration of radiation from the Therac-25 medical linear accelerator” (Death and Denial).

The first accident occurred on a 61-year old woman who was at a follow-up appointment after a breast tumor was removed. She felt a burning sensation and told the operator “you burned me”. She developed swelling and reddening, but the AECL declared this a normal treatment reaction and not a machine malfunction. Her condition wor...

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...perator, who again accidentally chose the wrong mode and used the up arrow and enter to correct the problem and administer the treatment. Again, the “malfunction 54” error message occured. The AV equipment was now working, and the operator heard a loud noise and a moan, which resulted in checking on the patient. The patient fell into a coma and died three weeks later (Death and Denial, The Accidents).

The sixth and final accident was supposed to receive small position verification doses. After the machine halted with an error message, the operator pressed the button to continue, and the machine displayed that it had delivered the correct dose. The patient complained of pain, and died from complications resulting from a radiation overdose three months later (Death and Denial, The Accidents).

Works Cited

http://users.csc.calpoly.edu/~jdalbey/SWE/Papers/THERAC25.html