This web page will send you to a series of pages that describe a case that Deborah Johnson and Keith Miller will discuss at the workshop. The case is one of those available on www.ComputingCases.org, namely the Therac 25 case. The introduction below is taken from the description of that case on the site.
Therac-25 was a new generation medical linear accelerator for treating cancer. It incorporated the most recent computer control equipment. Therac-25's computerization made the laborious process of machine setup much easier for operators, and thus allowed them to spend minimal time in setting up the equipment. In addition to making setup easier, the computer also monitored the machine for safety. With the advent of computer control, hardware based safety mechanisms were transferred to the software. Hospitals were told that the Therac-25 medical linear accelerator had "so many safety mechanisms" that it was "virtually impossible" to overdose a patient.
Normally, when a patient is scheduled to have radiation therapy for cancer, he or she is scheduled for several sessions over a few weeks and told to expect some minor skin discomfort from the treatment. The discomfort is described as being like a mild sunburn over the treated area. But in this case on safety critical software, you will find that some patients received much more radiation than prescribed
For background on this case, read the following documents. When you are done reading one document, return to this page using your BACK button, and then move on to the next page:
Now that you understand the basic setup of the machine and its operation, consider these accidents that occured at a cancer treatment facility in Tyler, Texas.
The Canadian Medical Company, after investigating the issue, discovered that there were some errors in the software that produced the problem. These errors and the fix they applied are described in the following document.
To open our workshop, Deborah Johnson and Keith Miller will role play two consultants who have been hired by the Canadian Medical Corporation. Their discussion will center on whether the software fixes described in the above document are sufficient to make the Therac-25 system marketable again. The main question: given these fixes, should the Canadian Medical Corporation tell facilities with Therac-25 machines that they can continue using the machine safely? If not, what should be done?