CASE STUDY NO.1
THERAC – 25
Aaron James Uy Timosa
BSIT – 4
The Therac-25 was a radiation therapy machine produced by Atomic Energy of Canada Limited (AECL) after the Therac-6 and Therac-20 units (the earlier units had been produced in partnership with CGR of France). It was involved in at least six accidents between 1985 and 1987, in which patients were given massive overdoses of radiation, approximately 100 times the intended dose. These accidents highlighted the dangers of software control of safety-critical systems, and they have become a standard case study in health informatics and software engineering.
WHAT WAS THERAC -25?
Therac-25 was used in the treatment of cancer. Its purpose was to provide radiation to a specific part of the body and hopefully kill the malignant tumor. The Therac-25 was the third system created under the Therac name by the Atomic Energy of Canada Limited (AECL). The AECL is most famous in Canada for their creation of the CANDU reactors which are world renowned. A Therac-6 and Therac-20 were both used in the treatment of cancer. The number that goes along with the word Therac stands for the maximum amount of mega electron volts (MeV) the machine can dispense. It was believed that the new Therac-25 was much more efficient than Therac-6 and Therac-20. The overall size of the machine was reduced and still allowed for two modes; photon mode and electron mode. A tungsten shield was in place for the X-ray mode and removed for the electron mode Between June 1985 and January 1987, a computer controlled radiation therapy machine, called the Therac-25, massively overdosed six people. These accidents have been described as the worst in the 35 year history of medical accelerators. A detailed accident investigation, drawn from publicly available documents, can be found in Leverson and Turner. The following account is take this report and includes both the factors involved in the overdoses themselves and the attempts by the users, manufactures and governments to deal with them. Because this accident was never officially investigated, some information on the Therac-25 software development, management, and quality control procedures are not available. What is included below has been gleaned from law suits and depositions, government records, and copies of correspondence and the other material obtained from the U.S Food and Drug Administration (FDA), which regulates these devices.
Atomic Energy of Canada Limited (AECL)
AECL is a Canadian federal Crown corporation and Canada's largest nuclear science and technology laboratory. AECL developed the CANDU reactor technology starting in the 1950s, and in October 2011 licensed this technology to Candu Energy (a wholly owned subsidiary of SNC-Lavalin). Today AECL develops peaceful
nd innovative applications from nuclear technology through expertise in physics, metallurgy, chemistry, biology and engineering. AECL's activities range from research and development, design and engineering to specialized technology development, waste management and decommissioning. AECL partners with Canadian universities, other Canadian government and private-sector R&D agencies (including Candu Energy), various national laboratories outside Canada, and international agencies such as the IAEA.
THERAC – 25 ERROR/S AND RESULT
The Therac-25 treatment system was first started in 1976 but was generally a piece of machinery. The software controlled system came online in 1982. The first incident occurred in 1985 and five more happened within 19 months of the original. After the fifth the Federal Drug Administration recalled Therac-25 until it was "fixed". Unfortunately the sixth incident occurred before the changes had been made. The first incident involved a 61 year old women from Marietta, Ga. who was receiving follow-up treatment after a tumor had been removed from her breast. Therac-25 administered a very large overdose of radiation and...
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