This is an abstract of a 1993 article from ieee computer about the therac25 computerized radiation therapy machine and its software flaws, which caused massive overdoses to patients. Since the time of the incidents related in this paper, aecl medical, a. Computers are increasingly being introduced into safetycritical systems and, as a consequence, have been involved in accidents. The therac25 was a computercontrolled radiation therapy machine produced by atomic. Therac25 and the security of the computer controlled. The therac25 was a computercontrolled radiation therapy machine produced by atomic energy of canada limited aecl in 1982 after the therac6 and therac20 units the earlier units had been produced in partnership with cgr of france. Case study therac25 page 1 of 3 therac25 the therac25 machine was a stateoftheart linear accelerator developed by the company atomic energy canada limited aecl and a french company cgr to provide radiation treatment to cancer patients.
The therac25 and its accident investigation several factors led to the thera25 accidents. On six separate occasions between june 1985 and january 1987, the therac25, a computercontrolled radiation therapy machine, is known to have killed or seriously injured patients in the us and canada with massive radiation overdoses. Between june 1985 and january 1987, the therac25 medical electron accelerator was involved in six massive radiation overdoses. An investigation of the therac25 accidents essay 10546. An investigation of the therac25 accidents computer. Their engineering method was poor, for instance, they assigned a single programmer to the daunting task of creating the machines real time software which was very complex. The second, higher energy mode, used the full power of the machine at 25 million electron volts. I do not own any of the images, music, or videos used. References to more recent accidents are included below. Sunday, march 29, 2020 the therac 25 had two main types of operation. Turner, university of california, irvine a thorough account of the therac25 medical electron accelerator accidents reveals previously unknown details and suggests ways to reduce risk in the future. These accidents have been described as the worst in the 35year history of medical accelerators 6. These socalled accidents and mistakes are really just cases of human inattention. An investigation of the therac25 accidents abstract.
An investigation of the therac25 accidents by nancy g. History of therac devices and accidents journey towards. An investigation of the therac25 accidents abstract online ethics center for engineering 2162006 oec accessed. An investigation of the therac25 accidents nancy leveson, university of washington clark s. It was involved in at least six accidents between 1985 and 1987, in which patients were given massive overdoses of radiation. The first mode consisted of an electron beam of 200 rads that was aimed at the patient directly. Nancy leveson and clark turner, the investigation of the therac25 accidents, computer, 26, 7 july 1993 pp 1841. System safety, and computers update of the 1993 ieee computer article addisonwesley.
Therac 25 accident report the cognitive systems engineering. The therac 25 accidents form the basis for what is often considered the bestdocumented software safety casestudy available. The therac25 and its accident investigation case study. The big picture the therac25 was a computerized radiation therapy machine 11 machines were installed us and canada in 19851987 there were 6 known accidents where massive overdoses were made patients died or suffered serious injuries these were traced to race conditions in reading operator input unique early investigation of safetycritical. Researchers who investigated the accidents found several contributing causes. An investigation of the therac25 accidents part iii nancy leveson, university of washington clark s. Pdf importance of software quality assurance to prevent. A case study of the therac25 chuck huff1 and richard brown2 abstract almost all computer ethics courses use cases to some extent. A detailed investigation of the factors involved in the softwarerelated overdoses and attempts by users, manufacturers, and government agencies to deal with the accidents is presented.
An updated version of the original accident investigation paper by nancy leveson i have updated and changed slightly the original accident report. The therac25 was a radiation therapy machine produced by atomic energy of canada limited aecl in 1982 after the therac6 and therac20 units the earlier units had been produced in partnership with cgr of france. A detailed investigation of the factors involved in the softwarerelated overdoses and attempts. A thorough account of the therac25 medical electron accelerator accidents reveals previously unknown details and suggests ways to reduce risk in the future. The experience illustrates a number of principles that are vital to understanding how and why the design and analysis of safetycritical systems must be done in a methodical way according to established principles. Some of the types of system problems found in the therac25 may be present in the medical radiation devices currently in use. The therac25 was a computercontrolled radiation therapy machine produced by atomic energy of canada limited aecl in 1982 after the therac6 and therac20 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. A detailed accident investigation, drawn from publicly. As a result, several people died and others were seriously injured. Therac25 was a medical linear accelerator, a linacdeveloped by atomic energy of canada ltdaecl. The ones marked may be different from the article in the profile. Fda memos accuses aecl by not having a mechanism to follow up reports of suspected accidents 4 after developing a reddening and swelling in the center of the treatment area, the patient was admitted to a hospital in atlanta, but was sent to kennestone to go on with therac25.
Therac25 was a radio therapy machine used to destroy tumors using high energy beams. The most serious computer related accidents to date. The therac25 was the most computerized and sophisticated radiation therapy machine of its time. Turner, university of california, irvine reprinted with permission, ieee computer, vol. The series of accidents has been described as the worst in the 35year history of medical accelerators. Oec an investigation of the therac25 accidents abstract. We show how we have integrated detailed historical cases into ethical reflection throughout the computer science.
However, in the case of therac25, they can be deadly. This cited by count includes citations to the following articles in scholar. The therac25 was a radiation therapy machine produced by atomic energy of canada limited aecl in 1982 after the therac6 and therac20 units the earlier units had been produced in. Company called atomic energy commision limited aecl and another french company called cgr were paired up to produce medical linear accelerators.
The therac 25 a case study in safety failure radiation therapy machine the most serious computerrelated accidents to date people were killed references. The manufacturers were responsible for many of these factors that eventually caused death to the victims. An investigation of the therac25 accidents stanford university. An investigation of the therac25 accidents cal poly computer. In the 1980s, a number of people were killed and injured by a flawed radiation therapy machine.
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