Social Impact Analysis
Ethics in Computing Links
Therac-25: A Socio-Technical System
The safety of the Therac-25 is not really a property of the machine alone.
Accidents that go unreported contribute to (or at least fail to stop)
later accidents. When the TV camera in the room is unplugged, the operator
cannot see that the patient is in trouble. So safety is really a property
of the entire technical and social system (socio-technical system). In
a similar manner, an ethical analysis of the issues in this case requires
an awareness of the entire socio-technical system.
The Therac-25 Medical Linear Accelerator is a large machine that sits
in a room designed just for it. We think of the machine itself or the
machine-in-the-room as the system. But the larger system, or the Socio-Technical
system, that we need to think about includes:
- Hardware: The mechanics of the machine itself, including its
- Software: the operating system of the computer and the operating
system of the machine
- Physical surroundings: the room with its shielding, cameras,
locking doors, etc.
- People: operators, medical physicists, doctors, engineers,
salespeople, managers at AECL, government regulators
- Institutions: AECL, FDA, each medical facility, associations
of operators, etc.
- Management models: AECLs model of how risk is managed
- Reporting relationships: who was required to report accidents
- Documentation requirements: for the software, for the facilities,
for the FDA
- Data flow: how different parts of AECL shared information,
how information was shared among agencies and organizations, how data
was used by the Therac software.
- Rules & norms: what patients are "normally"
told, what operator & physicist responsibilities are, expectations
set for the programmer
- Laws and regulations: Reporting requirements, FDA enforcement
mechanisms, medical liability law
- Data: data was collected in FDA approval process, use of data
in Therac software,
The following table presents some of these items in a schematic form.
The Socio-Technical System
- Supporting Systems (video, audio, etc.)
- Software Systems
Hospitals and Clinics
- Doctors, Medical Physicists
- Management, User Groups
- Operators, Reporting Procedures
Atomic Energy Canada, Limited
- Management, Reporting Procedures,
- Design Teams, Sales Staff, Support and Field Engineers
Government Medical Device Regulation
- Food and Drug Administration
- Canadian Radiation Protection Bureau
- Reporting Procedures
A thorough investigation of the Therac-25 case requires some grasp of
most of these items. You will come across most of these items as you read
this case. Setting your sights on the entire system will help you avoid
the trap of finding a single point of blame. It is easy, for instance,
to decide that the programmer made serious mistakes and to end ones
analysis there. This is a short-sighted approach. It would miss the problems
with maintenance in the cancer therapy facilities; it would miss the incomplete
reporting requirements for the FDA; it would miss the inadequate and misleading
testing of the Therac-25 system.