Therac-25
Therac-25
Therac-25 (/θɛræk 25/) is a radiotherapy machine that was involved in six known accidents between 1985 and 1987, due to a software bug.
Etymology
The term "Therac" is derived from "Therapeutic Accelerator", a name given to the machine by its manufacturer, Atomic Energy of Canada Limited (AECL). The number "25" refers to the machine's maximum radiation output of 25 million electron volts (MeV).
Description
The Therac-25 was a dual-mode machine, capable of producing either a direct beam of high energy electrons for superficial treatment, or X-rays for deep-seated tumors. The machine was controlled by a PDP-11 minicomputer, which also monitored various safety interlocks.
Accidents
Between 1985 and 1987, the Therac-25 was involved in six known accidents where patients were given massive overdoses of radiation. These incidents were caused by a software bug in the machine's control system, which allowed the high-energy electron beam to be delivered directly to the patient without the usual scattering device in place. The accidents led to significant changes in the regulation of medical devices and the practice of software engineering.
Related Terms
- Radiotherapy
- Software bug
- Atomic Energy of Canada Limited
- Electron
- X-ray
- PDP-11
- Software engineering
External links
- Medical encyclopedia article on Therac-25
- Wikipedia's article - Therac-25
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