Therac-25 was a medical linear accelerator used for radiation therapy treatment in the 1980s. It was designed and manufactured by Atomic Energy of Canada Limited (AECL). Unfortunately, the Therac-25 was involved in a series of accidents that led to patients receiving massive overdoses of radiation, resulting in serious injuries and fatalities.

The accidents were primarily caused by software and hardware design flaws. The Therac-25 used a dual-mode system that allowed it to operate in high-energy electron mode or photon mode. Switching between modes required reconfiguring the hardware, and the software controlled this process. However, due to coding errors, the system allowed the machine to deliver radiation at much higher doses than intended under certain conditions.

Additionally, the system did not provide adequate error messages or fail-safe mechanisms, making it challenging for the operators to detect the errors and stop the treatment before severe damage occurred. The lack of proper safety interlocks and user-friendly interfaces contributed to the accidents.

As a result of these tragic incidents and the lessons learned from them, the field of medical device design and safety underwent significant changes and improvements. The Therac-25 case has become a crucial example in the study of software engineering ethics and has had a lasting impact on safety protocols in medical device development and operation.