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Therac 25

Software Presentation

Era Eisieis

on 23 April 2013

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Transcript of Therac 25

Therac-25 Accidents 1) Kennestone Regional Oncology Center.
1985 2) Ontario Cancer Foundation, 1985. 3) Yakima Valley Memorial Hospital, 1985 4) East Texas Cancer Center, March1986. 5) East Texas Cancer Center, April 1986. 6) Yakima Valley Memorial Hospital,
1987. example of Radiation therapy safety-critical system death or serious injury to people, or
loss or severe damage to equipment or
environmental harm is a system whose failure or malfunction may result in: also life-critical system How can we prevent mistakes?

Linear accelerator to deliver x-rays and electron beams for the treatment of cancer

Released in 1985

Third generation machine (Therac-6, Therac-20) The standard approach is to carefully code, inspect, document, test, verify and analyze the system How to increase safety? Problems in the case Therac-25 poor software engineering practices

building a machine that relies on software for safe operation

a woman received treatment and got injured
she developed redding, swelling and her arm was immobile

instead of 200 rads she received over 10.000 rads seven weeks later ... a 40 year old woman came for her 24th treatment
again it had a malfunction

after 3 days the patient complained of
swelling, burning and hip pain

patient died around 4 months later of a viruent cancer
estimated 13.000 to 17.000 rads

AECL sparely informed users and improved a few hardware modules a woman came for treatmend
she developed reddings thereupon

survived the reactions of treatment
minor disability and scares a patient came for his 9th treatment

machine displayed underdose
patient received estimately 15.000-20.000 rads in 1 second

patient died because of complications around five months after the accident - documentation (inception, elaboration)
- semaphors
- modularisation
- testing
- software metrics
use design patterns! Requirements - identify attributes, capabilities, characteristics, or qualities of a system.

Architecture/Design - Overview of software and relations

Technical - Documentation of code, algorithms, interfaces, and APIs.

End User - Manuals for the end-user, system administrators and support staff. Documentation Thank you for your attention! Therac 25 and software bugs
Full transcript