Human Factors Risk Management as a Way to Improve Medical Device Safety: A Case Study of the Therac 25 Radiation Therapy System

Abstract

In a fatal incident in 1984 much discussed in the literature, a patient received 16,000 rads instead of the intended 180 rads when undergoing radiation treatment. This incident likely could have been prevented by the use of risk analysis. Risk analysis techniques to identify use errors have received increasing attention in health care. Use errors are defined as a pattern of predictable human errors that can be attributable to inadequate or improper design. Among the most widely used of the risk analysis tools are Failure Modes and Effects Analysis (FMEA) and fault tree analysis (FTA). The Therac 25 Radiation Therapy System incidents involved a combination of technical failures (software and possibly hardware) combined with human behavior resulting in catastrophic radiation overdoses. From a manufacturer's perspective, FMEAs and FFAs are valuable methods to systematically evaluate a medical device design's potential for inducing use errors. When these risk analyses are done early in the development cycle, potential faults and their resulting hazards are identifiable and much easier to mitigate with error-reducing designs. These risk management methods are excellent complements to other important user-centered design best practices.