Dimitrios Christias Robert Lyon Andreas Petrou

Dimitrios Christias Robert Lyon Andreas Petrou

Therac-25 is a computer-controlled radiation therapy machine that was designed by Atomic Energy of Canada Limited (AECL).

It was used in medical institutions to destroy tumors. Operates in a dual-mode. Depends more on software routines to ensure safety. Evolution of Software

Several accidents of radiation overdose happened between 1985 and 1987 using the Therac-25 due to software issues.

Therac-6

Therac-25

Therac-20

Concurrency problems- Therac-25 has a software system that allows concurrent access to shared memory.- The fundamental design of the system was flawed, as it lacked synchronization

Lack of safety - Therac-25 relied only on its software to ensure safety measures and handling

errors Lack of documentation - The system has been developed to display cryptic error messages - The user manuals did not indicate the danger of those malfunctions for the patient

health. Lack of testing - Limited and poor test coverage The user centred design

- User centred design concerns seemed to override patient safety The role of Government - No information of the development, management and quality control procedures

is available Ignorance of the incidents

- system users were unconcerned about the fact that Therac-25 was causing harm through its use

Adhere to basic principles of software engineering Proper testing Extensive documentation

Re-using codeArrogance in the assumption that the software is safeUnrealistic risk assessment Interface design that focused on usability rather than safety

Bozdag, E., 2009. Therac-25 and the security of the computer controlled equipment. [online], Ethics of Science and Technology. Available at <http://citeseerx.ist.psu.edu> [Accessed 01 October 2011].

Leveson, N., 1995. Medical Devices: The Therac-25. [online], University of Washington. Available at <http://sunnyday.mit.edu/papers/therac.pdf> [Accessed 01 October 2011].

Lim, J., 1998. An Engineering Disaster: Therac-25. [online], Available at <http://www.bowdoin.edu> [Accessed 01 October 2011].