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Module Activities:
1. Instructor introduces the case based on the abstract and timeline found at www.computingcases.org
2. Students read case abstract, timeline, case decision point, and case analysis exercises.
3. Students do further research into the case by consulting ComputingCases materials which include narratives,histories, supporting documents, and ethical analyses.
4. Students carry out the activities outlined in the accompanying case exercises by (a) specifying the problemraised in the decision point, (b) generating solutions, (c) testing solutions using ethics tests, and (d) developing plans forimplementing the solution over situational constraints.
5. Students prepare their case analyses working in small groups.
6. These groups present their completed analysis to the class in a case-debriefing session.
7. The instructor concludes by discussing the problem-solving issues and intermediate moral concepts raised bythe case.
Therac-25 was a new generation medical linear accelerator for treating cancer. It incorporated the most recent computer control equipment.Therac-25’s computerization made the laborious process of machine setup much easier for operators, and thus allowed them to spendminimal time in setting up the equipment. In addition to makingsetup easier, the computer also monitored the machine for safety. With the advent of computer control, hardware based safetymechanisms were transferred to the software. Hospitals were told that the Therac-25 medical linear accelerator had "so many safetymechanisms" that it was "virtually impossible" to overdose a patient. Normally, when a patient is scheduled to have radiationtherapy for cancer, he or she is scheduled for several sessions over a few weeks and told to expect some minor skin discomfort fromthe treatment. The discomfort is described as being like a mild sunburn over the treated area. But in this case on safety criticalsoftware, you will find that some patients received much more radiation than prescribed
| Early1970’s | AECL and a French Company (CGR) collaborate to build Medical Linear Accelerators (linacs). They develop Therac-6, and Therac-20.(AECL and CGR end their working relationship in 1981.) |
| 1976 | AECL developes the revolutionary "double pass" accelerator which leads to the development of Therac-25. |
| March, 1983 | AECL performs a safety analysis of Therac-25 which apparently excludes an analysis of software. |
| July 29,1983 | In a PR Newswire the Canadian Consulate General announces the introduction of the new "Therac 25" Machine manufactured byAECL Medical, a division of Atomic Energy of Canada Limited. |
| ca. Dec. 1984 | Marietta Georgia, Kennestone Regional Oncology Center implements the new Therac-25 machine. |
| June 3, 1985 | Marietta Georgia, Kennestone Regional Oncology CenterKatherine (Katy) Yarbrough, a 61-year-old woman is overdosedduring a follow-up radiation treatment after removal of a malignant breast tumor. Tim Still, Kennestone Physicist calls AECL asking ifoverdose is possible; three days later he is informed it is not. |
| July 26, 1985 | Hamilton, Ontario, Canada. Frances Hill, a 40-year-old patient is overdosed during treatment for cervical carcinoma. AECLis informed of the injury and sends a service engineer to investigate. |
| November 3, 1985 | Hamilton Ontario patient dies of cancer, but it is noted on her autopsy that had she not died, a full hip replacement wouldhave been necessary as a result of the radiation overdose. |
| November 8, 1985 | Letter from CRPB to AECL requesting additional hardware interlocks and changes in software. Letter also requested treatmentterminated in the event of a malfunction with no option to proceed with single key-stroke. (under Canada’s Radiation Emitting DevicesAct.) |
| November 18, 1985 | Katy Yarbrough files suit against AECL and Kennestone Regional Oncology Center. AECL informed officially ofLawsuit. |
| December 1985 | Yakima Valley Memorial Hospital, Yakima Washington. A woman being treated with Therac-25 develops erythema on her hip after oneof the treatments. |
| January 31, 1986 | Staff at Yakima sends letter to AECL and speak on the phone with AECL technical support supervisor. |
| February 24, 1986 | AECL technical support supervisor sends a written response to Yakima claiming that Therac-25 could not have been responsiblefor the injuries to the female patient. |
| March 21, 1986 | East Texas Cancer Center, Tyler Texas. Voyne Ray Cox is overdosed during treatment on his back. Fritz Hager notifies AECL.Company suggests some tests and suggests hospital might have an electrical problem. AECL claims again that overdoes is impossibleand that no other accidents have occurred previously. |
| March 22, 1986 | Ray Cox checks into an emergency room with severe radiation sickness. Fritz Hager calls AECL again and arranges for RandyRhodes and Dave Nott to test Therac. They travel to Texas and test Therac but find nothing wrong. |
| April 7, 1986 | ETCC has investigated electrical problem possibility, finding none, put Therac-25 back in service. |
| April 11, 1986 | East Texas Cancer Center. Another Verdon Kidd is overdosed during treatments to his face. Operator is able to explain howMalfuction 54 was achieved. Fritz Hager tests computer’s readout of no dose, and discovers the extent of the overdoses. Hager spendsweekend on phone with AECL explaining findings. |
| April 14, 1986 | AECL files report with FDA. AECL sends letter to Therac-25 users with suggestions for avoiding future accidents, including theremoval of the up-arrow editing key and the covering of the contact with electrical tape. |
| May 1, 1986 | Verdon Kidd, who was to have received treatments to left ear dies as a result of acute radiation injury to the right temporallobe of the brain and brain stem. He is the first person to die from therapeutic radiation accident. |
| May 2, 1986 | FDA declares Therac-25 defective, and their "fix" letter to users inadequate. FDA demands a CAP from AECL. |
| June 13, 1986 | AECL produces first CAP for FDA. |
| July 23, 1986 | FDA has received CAP, asks for more information. |
| August, 1986 | Therac-25 users create a user group and meet at the annual conference of the American Association of Physicists inMedicine |
| August, 1986 | Ray Cox, overdosed during back treatment, dies as a result of radiation burns. |
| September 23, 1996 | Debbie Cox and Cox family file lawsuit |
| September 26, 1986 | AECL provides FDA with more information. |
| October 30, 1986 | FDA requests more information. |
| November 1986 | Physicists and engineers from FDA’s CDRH conducted a technical assessment of the Therac-25 at AECL manufacturing plantin Canada (R.C. Thompson). |
| November 12, 1986 | AECL submits revision of CAP. |
| December | Therac-20 users notified of a software bug. |
| December 11, 1986 | FDA requests more changes to CAP. |
| December 22, 1986 | AECL submits second revision of CAP. |
| January 17, 1987 | Second patient, Glen A. Dodd, a 65-year-old man, is overdosed at Yakima. |
| January 19, 1987 | AECL issues hazard notification to all Therac-25 users and told them to visually confirm the position of the turntable beforeturning on beam. |
| January 26, 1987 | Conference call between AECL quality assurance manager and Ed Miller of FDA. AECL sends FDA revised test plan. AECL callsTherac users with instructions on how to avoid beam on when turntable is in field light position. |
| February 3, 1987 | AECL announces additional changes to Therac-25 |
| February 6, 1987 | Ed Miller calls Pavel Dvorak of Canada’s Health and Welfare department with news that FDA will recommend that all Therac 25units be taken out of service until CAP is completed. |
| February 10, 1987 | FDA sends notice to AECL advising that Therac is defective under US law and requesting AECL to notify customers that it shouldnot be used for routine therapy. Canadian Health Protection Branch does the same. |
| March 1987 | Second User Group Meeting |
| March 5, 1987 | AECL sends third revision of CAP to FDA. |
| April 1987 | Glen A. Dodd, overdosed at Yakima, dies of complications from radiation burns to his chest. |
| April 9, 1987 | FDA asks for additional information regarding third CAP revision. |
| April 13, 1987 | AECL sends update of CAP and list of nine items requested by users at March meeting. |
| May 1, 1987 | AECL sends fourth revision of CAP to FDA as a result of FDA commentary at user meeting. |
| May 26, 1987 | FDA approves fourth CAP subject to final testing and analysis. |
| June 5, 1987 | AECL sends final test plans to FDA along with safety analysis. |
| July, 1987 | Third Therac-25 User Group Meeting |
| July 21, 1987 | AECL sends final (fifth) CAP revision to FDA. |
| January 28, 1988 | Interim safety analysis report issued from AECL. |
| November 3, 1988 | Final safety analysis report issued. |
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