1. Dimitrios Christias Robert Lyon Andreas Petrou COMP60611: Fundamentals of Parallel and Distributed SystemsDirect Reading 1 – Therac-25

2. 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. Introduction Therac-6 Therac-20 Therac-25

3. 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 Causes of accidents

4. Adhere to basic principles of software engineering • Proper testing • Extensive documentation • Re-using code • Arrogance in the assumption that the software is safe • Unrealistic risk assessment • Interface design that focused on usability rather than safety conclusion

5. 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]. references