Therac25 aecl designed therac25 to use computer control from the start. The therac25 and its accident investigation case study 1. It was involved in at least six accidents between 1985 and 1987, in. However, aecl designed the therac 25 to take advantage of com puter control from the outset. An investigation of the therac25 accidents between june 1985 and january 1987, 6 known accidents. 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 fda investigation was well under way when aecl produced a medical device report to discuss the details of the radiation overexposures at tyler. Some of the most widely cited softwarerelated accidents in safetycritical systems involved a computerized radiation therapy machine called the therac25.
Because this accident was never officially investigated, some information on the therac25 software development, management, and quality control procedures. An investigation of the therac25 accidents computer. A thorough account of the therac25 medical electron accelerator accidents reveals previously unknown details and suggests ways to reduce risk in the future. A detailed accident investigation, drawn from publicly. An investigation of the therac25 accidents stanford university. Pdf importance of software quality assurance to prevent. The therac25 and its accident investigation case study. Briefly, the therac 25 was a medical radiation therapy machine that was supposed to deliver controlled doses of radiation to cancer patients. Therac25 was a radio therapy machine used to destroy tumors using high energy beams. Researchers who investigated the accidents found several contributing causes. As a result, several people died and others were seriously injured.
Turner, an investigation of the therac25 accidents, computer, 26 july 1993. An investigation of the therac25 accidents part iii. Citeseerx an investigation of the therac25 accidents. Therac 6 and therac 20 had histories of clinical use without computer control therac25 software had more responsibility for safety than in previous machines. The therac 25 a case study in safety failure radiation therapy machine the most serious computerrelated accidents to date people were killed reference. Therac25 was a medical linear accelerator, a linacdeveloped by atomic energy of canada ltdaecl. The first mode consisted of an electron beam of 200 rads that was aimed at the patient directly. A history of the introduction and shut down of therac25. This provided the economic advantage of delivering two kinds of therapeutic radiation with one machine. An investigation of the therac 25 accidents nancy leveson, university of washington clark s.
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. 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. The most serious computer related accidents to date. The manufacturers were responsible for many of these factors that eventually caused death to the victims. Although the authors warn against drawing any oversimplified conclusions from these complex accidents, it appears clear to me that the root cause was the omission from the therac25 of the hardware safety interlocks of its safely operated predecessor, the therac20, and the devices dependence for these functions on poorly written, hardly. I besides citing the awed microswitch, i the report faulted both hardware and software components of the theracs design. The therac25 is a radiation therapy machine used during the mid80s. 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. I do not own any of the images, music, or videos used. The therac25 was a computercontrolled radiation therapy machine produced by atomic. First, like the therac 6 and the therac 20, the therac 25 is controlled by a pdp 11.
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. Therac25 and the security of the computer controlled. Citeseerx document details isaac councill, lee giles, pradeep teregowda. Although the authors warn against drawing any oversimplified conclusions from these complex accidents, it appears clear to me that the root cause was the omission from the therac25 of the hardware safety interlocks of its safely operated predecessor, the therac 20, and the devices dependence for these functions on poorly written, hardly. I it concluded with a list of four modi cations to the therac25 necessary for minimum compliance with canadas radiation emitting devices red act which gave government o cials. 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. 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 contents. Software in the therac 6 and therac 20 was reused in the therac25. Therac 25 background medical linear accelerator developed by atomic energy of canada, ltd.
The therac 25 a case study in safety failure radiation therapy machine the most serious computerrelated accidents to date people were killed references. Essay on the therac25 and its accident investigation instructor name school coursenumber june 2, 2015 introduction in 1983, a machine was released to help in the studentshare our website is a unique platform where students can share their papers in a matter of giving an example of the work to be done. These accidents have been described as the worst in the 35year history of medical accelerators 6. The second, higher energy mode, used the full power of the machine at 25 million electron volts. Therac25 radiation overdoses your expert root cause. In 1982 a machine called therac25 created by the atomic energy of canada limited aecl appeared in the medical field for cancer treatments, using radiation and x. The fda declared the therac25 defective under the radiation control for health and safety act and. An investigation of the therac25 accidents essay 10546. Therac6 and therac20 had histories of clinical use without computer control therac25 software had more responsibility for safety than in previous machines. Oec an investigation of the therac25 accidents abstract. Many lessons can be learned from this series of accidents.
Nancy leveson and clark turner, the investigation of the therac25 accidents, computer, 26, 7 july 1993 pp 1841. Nancy leveson and clark turner, the investigation of thetherac 25 accidents, computer, 26, 7 july 1993 pp 1841. It delivered two types of radiation beams, a lowpower electron beam and a highpower xray. With the aid of an onboard computer, the device could select multiple. In the 1980s, a number of people were killed and injured by a flawed radiation therapy machine. An investigation of the therac25 accidents cal poly computer. Between june 1985 and january 1987, the therac25 medical electron accelerator was involved in six massive radiation overdoses. A common mistake in engineering, in this case and in many others, is to put too much confidence in software. Turner, university of california, irvine reprinted with permission, ieee computer, vol. Several fcatures of the therac 25 are important in understanding the acci dents.
Ppt therac 25 powerpoint presentation free to view. The therac 25 accidents came at a time before many current practices were widespread, and serve as a cautionary tale for why such practices exist and are essential to creating safe systems. Name instructors name course date the therac25 and its accident investigation several factors led to the thera25 accidents. Turner, an investigation of the therac25 accidents, in ethics and computing. Untitled the cognitive systems engineering laboratory at ohio. Software in the therac6 and therac20 was reused in the therac25. However, in the case of therac25, they can be deadly. The therac 25 was a computercontrolled radiation therapy machine produced by atomic energy of canada limited aecl in 1982 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. An updated version of the original accident investigation paper by nancy leveson i have updated and changed slightly the original accident report. An investigation of the therac25 accidents part iii nancy leveson, university of washington. An investigation of the therac25 accidents nancy leveson, university of washington clark s. Computers are obviously very beneficial in the medical field.
An investigation of the therac25 accidents nancy g. Computers are increasingly being introduced into safetycritical systems and, as a consequence, have been involved in accidents. The use of computers in the medical field is becoming more and more widely used. The therac25 was the most computerized and sophisticated radiation therapy machine of its time.