Unit 16: Therac-25 Radiation Overdose Crises (1985–1987) | STEM Case Study

Investigate the most infamous software bug in medical history with this complete 6-page printable STEM Case Study Packet! Designed specifically for middle and high school classrooms, this unit provides a deep, informative look at the 1985–1987 Therac-25 Radiation Overdose Crises, software race conditions, removal of mechanical hardware interlocks, arithmetic variable overflow errors, human-computer interface (HCI) flaw patterns, and biomedical device safety ethics. What’s Included in this 6-Page Deep-Dive Packet: Page 1: Historical Case Study & Technical Breakdown – Full historical narrative of the 6 fatal radiation overdose accidents across clinics in the US and Canada, computer-controlled medical linear accelerator mechanics, removal of backup mechanical relays, PDP-11 assembly code race conditions, "Malfunction 54" screen alerts, and comprehension check questions. Page 2: Day in the Life Scenario Challenge – Students step into the shoes of a Hospital Medical Physicist at Tyler, Texas in March 1986, analyzing operator fast-keying logs, turntable positioning timing windows, uncalibrated dose spikes, and device shutdown protocols. Page 3: Hands-On Unplugged Simulation & Applied Math – Simple step-by-step math calculations comparing high-current raw electron beam power vs low-current X-ray target beam power, radiation dose multiplication factors (Rads), and 1-byte integer counter overflow timing windows (0-255 rollover). Page 4: Engineering Ethics & Workplace Dilemma – Software code reuse vs medical device safety testing: analyzing AECL's initial denial of software bugs, blaming human operators for "Malfunction 54" errors, re-using Therac-6 assembly code without verification, and FDA recall authority reform. Page 5: Redesign Brief & Innovation Lab – Creative blueprinting assignment where students design "Therac-25 Medical Linac V-2," featuring independent hardware-limit interlocks, redundant optical turntable position switches, secondary watchdog microcontroller circuits, and fail-safe UI keypress delay buffers. Page 6: Teacher Answer Key & Scoring Rubric – Complete answer key for all questions and math problems, plus a 10-point grading rubric on Page 6 for evaluating student work on Page 5. Teacher Benefits: 100% Unplugged & Copy-Paste Friendly – Clean text layout with zero dark background boxes, code block syntax, or special math symbols for seamless editing in Word, Google Docs, or Canva. Multi-Day Classroom Value – Covers 3 to 5 full class periods; perfect for Computer Science, Physical Science, Biomedical Engineering, Health Science, CTE electives, or emergency sub plans. Highly Engaging Content – Combines radiation dosage math, assembly code logic simulation, hospital diagnostic roleplay, software safety ethics, and medical device redesign!