Between 1985 and 1987, a machine built to treat cancer delivered massive radiation overdoses to six patients across North America. Three of them died.
The earlier machines in its family had physical interlocks — metal and copper whose only job was to make the dangerous beam electrically impossible unless the target was in place. The Therac-25 was a new design, and those guards were never carried over. The job was given to the software instead.
The Magnanimous Doctor Warthan opens the file with the humour set aside: the eight-second typing window, the error message that meant nothing, the machine that cried wolf so often it destroyed its own ability to raise an alarm — and a manufacturer that wrote, twice, in formal letters, that an overdose was not possible, after patients had already been hurt.
Technical details drawn from Nancy Leveson and Clark Turner’s investigation, IEEE Computer, July 1993.
The Doctor’s voice and the Society’s imagery are synthesized.