Case Study #1 - The Therac-25
(Revised 27 January 2009)
Background
The Therac-25 was a medical radiation machine used to diagnose and treat cancer. It was first used in 1983. A very advanced machine at the time, the Therac-25 made extensive use of computer control to enable the machine to be operated more efficiently and to implement safety checks. The safety checks were especially important because the machine was used both for diagnostics (to make X-ray images of patients) and to apply radiation therapy, using X-rays and/or electron beams, to treat cancer. In several incidents, malfunctions which involved the machine's control system caused patients to receive much higher doses of radiation than intended. Some patients died and others were severely injured. The incidents were not the result of only one cause but instead resulted from a set of problems involving the machine hardware and software, the operating procedures of hospitals in which the
machines were used, the reaction of the manufacturing company, and the engineers who worked on the machine. Studying this case helps to shed light on the responsibility of the engineer not just as a technical professional but also as a member of the social environment in which the engineered system must work, and the need for engineers to understand the other persons who are involved. Who is ultimately responsible for the safe operation of the machine? Does the engineer have a responsibility to protect others from their own negligence or the negligence of third parties? Is it an engineer's duty to protect the public from possible negligence of the engineer's employer? An important secondary issue is one of public policy. Medical doctors are bound by the famous Hippocratic Oath, which has been summarized by the rule "A doctor must not harm patients." Society seems to interpret this rule as implying that every possible effort must be made to prevent accidents such as those which occurred when Therac-25 machines malfunctioned. However, the attempt to prevent all accidents has increased the cost of much medical equipment to very high levels, so high that many members of society cannot the medical care which these machines help provide. Ifan inexpensive machine could bring care to a million people who could not otherwise afford it, but would likely malfunction and hurt or kill a hundred, should such a machine be allowed to be used? Is the Hippocratic Oath an optimal rule for protecting patients, or doctors? Should engineers follow a similar rule, or should we allow ourselves to cause some harm if the net effect of our actions will be positive?
References
An overview with much discussion about the ethics of the case:
A more technically oriented discussion including details of some injuries: