Therac-25 Case Study: Defending the Operator's Actions and Ethics

This case study examines the ethical implications surrounding the Therac-25 incident, focusing on the role and responsibilities of the machine operator. The Therac-25, a computerized radiotherapy machine, administered excessive radiation doses to patients due to software failures and removed safety interlocks, resulting in injuries and deaths. The analysis defends the operator, arguing they acted ethically within their capacity, following procedures and lacking knowledge of potential overdose risks. The study highlights the failures of CMC, FDA and hospital administration, emphasizing the need for rigorous software quality assurance, transparent reporting of device failures, and clear communication of malfunction codes to prevent future accidents. The conclusion emphasizes the importance of stakeholder accountability and comprehensive safety measures in safety-critical systems.

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Therac-25 Case Study
The widely cited Human-Computer Interface accidents that relates to safety-critical
systems are the recorded misfortunes of the massive radiation overdoses of six patients by the
Therac-25 machine between 1985 and 1987. The computerized radiotherapy machine
administered a hundred times the standard therapeutic dose. The device was an updated version
of Therac-6 and Therac-20, but its incorrect system architecture resulted in software failure as
the engineers removed both the manual controls and hardware interlocks (Holzmann 16).
Patients were reporting burns that ultimately resulted in deaths and injuries. However, the
operators are not to blame for these accidents are they acted ethically.
BACKGROUND INFORMATION THE OPERATOR
Machine operators were the least in control of the Therac-25 being used at the facility. The CMC
manufactured the machine; the FDA approved it; the hospital accepted to use it in their facility
(Rae 3). An operator works for the hospital and does not play a part in the decision for the
machine to be used at the hospital. The hospital employs an operator to complete whatever tasks
the administration asks them to do; they don’t have the liberty to do otherwise. In case of a
lawsuit of anything legal, they are not at fault because they have an authority that tells them to
complete the scheduled treatments within specific days.

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For the Therac-25 case, the operator controlled the radiotherapy instrument using the
DEC VT100 terminal (Holzmann 18). During treatment, the operator positioned patients on the
therapy table, set the gantry rotation and electric field sizes manually, and attached all the
required accessories to the machine. The operator then left for the VT100 console to enter the
patient’s identity, gantry rotation, electronic field, and the treatment prescription, which included
the dose rate, time and the energy mode (Leveson 9). A patient’s treatment was permitted if the
manually set data compares with that at the console. Equally, the therapy is aborted if a
mismatch occurs, and only proceeds if the error is corrected.
INCIDENT INVOLVING THE OPERATOR
THowever, the operators complained about how long it took to feed in the treatment plan. In
response, the CMC modified the console interface to allow carriage returns to complete the
treatment data entry (Griffith Angela par.2). This modified interface would make the operator
tolerant of error messages, and readily allowing them to resume treatment. The interface did not
distinguish between life-threatening and minor errors but only when significant errors did not
prompt the “proceed” command (Rae 6). Despite the frequent machine errors and frequent
shutdowns, there was no information regarding the likeliness of an overdose.
REMEDIES FOR THE PROBLEM
It is essential that such erroneous malfunctions must be eliminated to avoid injury or deaths.
Nations ought to establish rigorous software quality assurance standards, which will ensure that
manufacturers perform tests to ascertain that their machines are safe. Stress tests and fault
injection can help detect any software’s bug or malfunction during the various testing levels
(Spichkova 309). Besides, the manufactures should report any failure on their devices to an
oversight authority and indicate the possibility of damage or injury to users. Equally important,

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the engineers ought to avoid sophisticated coding practices; for instance, an operator’s manual
ought to explain the meaning the malfunction codes (Spichkova 311). Additionally, other
stakeholders such as the operators or hospital administration ought to report any technicalities on
radiation machines to authorities such as the FDA.
ETHICAL ANALYSIS
According to Leveson, Spinello asserts that ethics make humans behave honorary to attain the
needs that make them more human (p.10). Spinello’s framework in ethical analysis recommends
considering moral intuitions on actions; whether they are right or wrong (Leveson p.Leveson
10). In the Therac-25 case, the operators ensured that all the treatments were done as scheduled.
Besides, they became insensitive to the frequent malfunction errors as technicians would fix the
mistakes, and the machine became operable again (GriffithAngela par.6). The operator’s manual
did not outline the possibility that the patients would be saturated in case of any malfunction
errors (Acharyulu and Seetharamaiah 139). More also, from the various safety mechanisms, the
machine operator believed that it was practically impossible to overdose patients during
radiotherapy. The operator acted on their capacity to treat cancer using the Therac-25 machine
without any knowledge of possible overdoses that would cause death or injury to patients.
CONCLUSION
The TTherac-25 incident shows the need to build future critical systems. The hospital
administration and FDA are accountable for these accidents in as much as the manufacturers are
held responsible too. However, the operator acted ethically in their role to the hospital in
administering radiation therapy to cancer patients. The operator’s responsibility to the
administration was to ensure that the machine was corrected by the technicians in case of any
malfunctions. Despite following the procedures, the device overdosed a patient in the instance of

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an error. Therefore, it is essential that all the stakeholders ensure that machine errors are reported
to the corresponding authorities to avoid accidents as in the case of the Therac-25 incident.
Works Cited
Acharyulu, PV Srinivas, and P. Seetharamaiah. “A framework for safety automation of safety-
critical systems operations.” Safety Science 77 (2015): 133-142
Griffith, Angela. Therac-25 Overdoses. 5 June 2017. www.<http://root-cause-analysis.therac-25-
radiation-overdoses/>. Accessed 18 March 2019
Holzmann, Gerard J. "Code Craft." IEEE Software 34.2 (2017): 18-21
Leveson, Nancy G. "The Therac-25: 30 Years Later." Computer 50.11 (2017): 8-11
Rae, Andrew. “Tales of disaster: the role of accident storytelling in safety teaching.” Cognition,
Technology & Work 18.1 (2016): 1-10.
Spichkova, Maria. "Design of formal languages and interfaces. "formal" does not mean
"unreadable"." Emerging Research and Trends in Interactivity and the Human Computer
Interface .Interface. IGI Global, 2014: 301-314.