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From all analysis, Therac-25 should be

Software quality assurance practices and standards should be established.

Designs should be kept simple and ensure user-friendly interfaces

Ways to get information about errors, i.e., software audit trails should be designed into the software from the beginning.

The software should be subjected to extensive testing and formal analysis at the module and software level.

System testing alone is not adequate; verification would be very valuable.

Involve users at all phases product development

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Error message provide by Therac 25 monitor are not helpful to operators

Machine pauses treatment but does not indicate reason why

The equipment control task did not properly synchronize with the operator interface task, so that race conditions occurred if the operator changed the setup too quickly.

Software is required to monitor several activities simultaneously in real time

Interaction with operator

Monitoring input and editing changes from an operator

Updating the screen to show the current status of machine

There were no independent checks that the software was operating correctly (verification)

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At first AECL denied that the Therac-25 was capable of delivering an overdose of radiation. The machine had so many safeguards in place that it frequently threw error codes and paused treatment, giving less than the prescribed amount of radiation

AECL carefully ran test after test and could not reproduce the error. The only possible cause they could come up with was a temporary failure in the three microswitches which determined the turntable’s position. The microswitch circuit was re-designed such that the failure of any one microswitch could be detected by the computer. This modification was quickly added and was in place for the rest of the accidents.

The Therac-25 displayed a “Malfunction 54” message. The message was not mentioned in the manuals. AECL explained that Malfunction 54 meant that the Therac-25’s computer could not determine if there a underdose OR overdose of radiation.

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At East Texas Cancer Center,patient complains of a bright flash of light, heard a frying, buzzing sound, and felt a thump and heat like an electric shock.

This indicates radiation overdose by Therac-25 machines after cancer treatment session

A few days after the unit was put back into operation, another patient complained that his face felt like it was on fire.

Another potential overdose of radiation beam by Therac-25.

Both patients died after 4months and 3 weeks respectively due to administered overdose of radiation

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Early 1970,AECL(Atomic Energy of Canada Limited) and a French Company (CGR) collaborate to build Medical Linear Accelerators (linacs).

They develop Therac-6, and Therac-20.

AECL and CGR end their working relationship in 1981.

In 1976, AECL develops the revolutionary "double pass" accelerator which leads to the development of Therac-25.

In March, 1983, AECL performs a safety analysis of Therac-25 which apparently excludes an analysis of software.

Medical linear accelerators (linacs) known generally as “Therac-25”.

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The Therac-25 was a medical linear accelerator, used to treat cancer patients to remove tumor.

Medical linear accelerators accelerate electron to create high-energy beams that can destroy tumors with minimal impact on surrounding healthy tissue

Shallow tissue is treated with accelerated electrons

Scanning magnets placed in the way of the beam; the spread of the beam (and thus its power) could be controlled by a magnetic fields generated by these magnets

Deeper tissue is treated with X-ray photons

The X-ray beam is flattened by a device in the machine to direct the appropriate intensity to the patient.

Beams kill (or retard the growth of) the cancerous tissues