The Therac-25 Disasters
How Software Bugs Killed Patients and Created Software Safety

About this book:

They walked into treatment rooms expecting healing. They walked out with radiation burns so severe their flesh sloughed from bone—or they didn’t walk out at all. Between 1985 and 1987, the Therac-25, a state-of-the-art cancer therapy machine, delivered lethal overdoses up to 100 times the prescribed dose. The culprit wasn’t a worn gear or a frayed wire—it was a few thousand lines of assembly code running on a DEC PDP-11. A race condition triggered by a fast-typing operator. An arithmetic overflow in a single-byte counter. The engineers had replaced physical safety interlocks with software, believing code couldn’t rust, couldn’t fail. They were wrong. This is the definitive account of how microscopic logic errors became macroscopic tragedies, told through the eyes of the victims, the investigators who fought institutional denial, and the regulators who were forced to rewrite the rules of software engineering forever.

*The Therac-25 Disasters* takes you inside the treatment rooms of Marietta, Tyler, and Yakima; into the PDP-11 assembly where the bugs lay dormant for years; and behind the closed doors where Atomic Energy of Canada Limited chose silence over safety. You’ll witness Nancy Leveson’s groundbreaking investigation that shattered the myth of "user error," the FDA’s unprecedented regulation of software as a medical device, and the painful birth of modern safety-critical standards. Every chapter reveals a new layer of the catastrophe—why unit testing missed the fatal flaws, how corporate culture normalized deviance, and why the distinction between software reliability and system safety is the line between life and death.

This isn’t just history. It’s the operating manual for the algorithmic age. The same design assumptions that killed Therac-25 patients now govern your pacemaker, your airplane’s flight controls, your autonomous vehicle, and the AI systems making life-or-death decisions in hospitals today. If you write code, manage engineers, regulate technology, or simply trust your life to software, this book is your most essential reading. The Therac-25 didn’t just change how we build medical devices—it changed how we understand the terrifying power of invisible logic. Read it before the next machine teaches us the same lesson.