Therac-25

• Medical Linear Accelerator
• Mechanical restrictions were removed in favour of software control
  • Originally restricted operability from the Therac-20 and Therac-6
• Programmed by one person
  • Minimal testing
  • Software designed without consideration of error handling
  • Software was not reviewed

1985 - Overdose of 100x the intended amount

• Software Issue

  • Race condition
  • If the operator entered inputs too fast, the list of configurations will be malformed
  • Issue wasn't discovered earlier as it required the operator to be proficient

• As a result of previous successful machines, the AECL believed in the safety.

Blame??

• Developers
• AECL (Business)
• Operator
• FDA (Regulators)

How much is a human life worth?

• This isn't the right question to ask
• What's the purpose of the product - to save humans