Case Study: Therac-25 - Software, Safety, and Medical Device Failures

This case study report examines the Therac-25, a computer-controlled radiation therapy machine manufactured by AECL, and the accidents that resulted from its use. The machine, installed in the USA and Canada, caused six massive radiation overdose incidents between June 1985 and January 1987. The malfunctions were primarily attributed to faulty software, with the machine's turntable position being a critical factor. The report highlights that AECL's initial safety measures were insufficient, particularly in software testing, and that over-reliance on the software contributed to the accidents. The report also notes that the FDA responded reactively to the incidents and recommended permanent modifications or shutdown of the machine. The case study emphasizes the importance of rigorous software testing and quality assurance in medical devices to prevent future tragedies.

Running head: REVIEW OF THERAC 25 CASE STUDY
REVIEW OF THERAC 25 CASE STUDY
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1REVIEW OF THERAC 25 CASE STUDY
This case study report is about the accidents caused by a computer controlled
radiation machine used for therapy called Therac- 25. These machines were created by the
Canadian corporation known as AECL. A total of eleven of these machines were installed in
USA and Canada together. This is one of the worst case of accidents in medical history which
caused six massive case of radiation overdose. The accidents happened in the time frame of
June, 1985 to January 1987 (Leveson, 1995). It has been reported that the machine’s turntable
position played a vital role in this accidents. Initial safety measure for this machine gave it
error free report but it did not test its software part and made several assumptions. The reason
behind these accidents is the malfunctioning of its controlling software. The software was
faulty and AECL neglected to assess its software properly before installation. Hence, AECL
should be blamed for these accidents. Another reason which have comes forth from this
report is that the people’s overdependence on the machine’s software. Additionally, the
quality assurance managers of the AECL mistook the machines reliability as its safety
measure. The error in software is expected and common for any computer controlled machine
and detailed analysis revealed that previous version of this machine, Therac- 20, also had
faulty software (Miller, 1987). Thus, these accidents could have been avoided if the quality
managers of AECL did not depended on the assumptions and actually conducted the software
test before installation. FDA acted to these accidents reactively and after the first incidents
declared the machine ineffective for service and after thorough investigation suggested
shutdown of these machine until permanent modification.

2REVIEW OF THERAC 25 CASE STUDY
References:
Leveson, N. (1995). Medical devices: The therac-25. Appendix of: Safeware: System Safety
and Computers.
Miller, E. (1987). The Therac-25 experience. Conference of State Radiation Control
Program Directors.