Transcript Διαφάνεια 1 - University of Manchester

Dimitrios Christias
Robert Lyon
Andreas Petrou
COMP60611: FUNDAMENTALS OF PARALLEL
AND DISTRIBUTED SYSTEMS
DIRECT READING 1 – THERAC-25
INTRODUCTION
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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
Therac-6
Software
Therac-20
Therac-25
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Several accidents of radiation overdose happened between 1985 and 1987
using the Therac-25 due to software issues.
CAUSES OF ACCIDENTS
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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
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Lack of safety
- Therac-25 relied only on its software to ensure safety measures and handling errors
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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.
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Lack of testing
- Limited and poor test coverage
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The user centred design
- User centred design concerns seemed to override patient safety
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The role of Government
- No information of the development, management and quality control procedures is available
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Ignorance of the incidents
- system users were unconcerned about the fact that Therac-25 was causing harm through its
use
CONCLUSION
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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
REFERENCES
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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].
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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].
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Lim, J., 1998. An Engineering Disaster: Therac-25. [online], Available
at <http://www.bowdoin.edu> [Accessed 01 October 2011].