archive-org.com » ORG » C » COMPUTINGCASES.ORG

Total: 197

Choose link from "Titles, links and description words view":

Or switch to "Titles and links view".
  • Daniel McCarthy Accident Accounts
    key The Therac 25 shut down within a few seconds making a noise audible through the newly repaired intercom The Therac monitor read Malfunction 54 The operator rushed into the treatment room and found McCarthy moaning for help He said that his face was on fire The hospital physicist was called McCarthy said that something had hit the side of his face and that he had seen a flash of light and heard a sizzling sound After this second accident at the hospital the ETCC physicist took the Therac 25 out of service and called AECL He worked with the Therac operator who had been administering treatment to both Dahl and McCarthy when the accidents occurred The physicist and the operator were eventually able to reproduce a Malfunction 54 They found that the malfunction occurred only if the Therac 25 operator rapidly corrected a mistake The ETCC physicist notified AECL of this discovery and AECL was eventually able to reproduce the error AECL advised Therac 25 users to physically remove the up arrow key as a short term solution AECL also filed a report with the United States FDA as required by law and began work on fixing the software

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/daniel_mccarthy.html (2016-04-30)
    Open archived version from archive


  • Anders Engman Accident Accounts
    turntable to the proper position for treatment Outside the treatment room the Therac 25 s control console read beam ready and the operator pressed the B key to turn the beam on The beam activated but the Therac 25 shut down after about 5 seconds The console indicated that no dose had been given so the operator pressed P to proceed with the treatment The Therac 25 shut down again listing flatness as the reason for treatment pause Engman said something over the intercom but the operator couldn t understand him The operator went into the treatment room to speak with Engman Engman told the operator that he had felt a burning sensation in the chest The operator s console displayed only the total dose of the two earlier treatments 7 rads Later that day Engman developed a skin burn over the treatment area Four days later the burn was striped in a manner similar to that of Janis Tilman s burn after she had been treated at Yakima the year before AECL investigated the accident All users were again told to visually confirm turntable setting before proceeding with any treatment Given the information it was suspected that the electron

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/anders_engman.html (2016-04-30)
    Open archived version from archive

  • Therac_25 Timeline
    Hospital Yakima Washington A woman being treated with Therac 25 develops erythema on her hip after one of 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 responsible for 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 impossible and 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 Randy Rhodes 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 how Malfuction 54 was achieved Fritz Hager tests computer s readout of no dose and discovers the extent of the overdoses Hager spends weekend 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 the removal 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 temporal lobe 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 in Medicine 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 plant in 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

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_resources/Timeline.html (2016-04-30)
    Open archived version from archive

  • Therac Case Glossary
    a potential of one volt Gantry the turntable assembly GAO and Comptroller General The General Accounting Office is the investigative arm of the Congress and is charged with examining all matters relating to the receipt anddisbursement of public funds The General Accounting Office GAO was established by the Budget and Accounting Act of 1921 31 U S C 702 to independently audit Government agencies Over the years the Congress has expanded GAO s audit authority added new responsibilities and duties and strengthened GAO s ability to perform independently The Office is under the control and direction of the Comptroller General of the United States who is appointed by the President with the advice and consent of the Senate for a term of 15 years Kludge or Kluge a computer system made up of poorly matched components medical linear accelerato r a device that accelerates electrons to create an electron beam Operator the individual responsible for the facitily room and preparing the Therac 25 machine for a particular patient Potentiometer a device that independently monitors turntable position rad radiation absorbed dose the amount of radiation that is absorbed by tissue in a treatment Acceptable level for single treatment is around 200

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_resources/Therac%20Glossary.html (2016-04-30)
    Open archived version from archive

  • Quality of Life
    life consideration AECL did not set out to make a device that would expose individuals to harm It made improvements in a device that would in theory allow greater access to a medical technology and would increase the quality of care those patients received In our interview with a Therac operator you can find testimony about the increased quality of life provided for operators and patients by the new machine

    Original URL path: http://computingcases.org/case_materials/therac/analysis/Quality_of_Life.html (2016-04-30)
    Open archived version from archive

  • Power
    using their products Ford Motor Company made itself infamous by explicitly comparing risk to the company in dollars lost from lawsuits to risk that consumer faced from inadequate design of gas tanks in the Pinto They decided that it would cost less to pay the lawsuits than to fix the car Here the calculations were all financial But it is at least up for debate whether all companies make decisions in this manner In many the motives are mixed protection of the company and safety of the consumer But AECL s priority seems odd even in the light of self protection Its risk analysis seemingly was not done to protect the company but to certify their already strongly held belief that the machine was safe This sort of unfounded optimism regarding technology at least provides them with the defense of ignorance But this defense is less persuasive when offered by those with power over other s well being Often when individuals or corporations are given more power we are also more likely to hold them more responsible for their actions At any rate this case is clearly an issue of who has power to enforce the acceptance of risks on others This power may be economic as in the case of AECL or political as in the FDA But at the individual level the power may simply be positional acquired because you happen to be the software engineer assigned to a particular project This is what Huff has called unintentional power the power that a designer has over the users of a product Someone with unintentional power uses it without intending benefit or harm to the ultimate user of the product This is another case of the defense of ignorance In this case the defense is harder to believe since

    Original URL path: http://computingcases.org/case_materials/therac/analysis/Power.html (2016-04-30)
    Open archived version from archive

  • System Safety
    might be responsible for the errors even though they were the ones to press the key An interesting issue arises because of the current move among operators to become more professionalized As operators are better trained are certified and are more aware of the workings of the machine they gain the prestige but they also gain responsibility As they become well trained enough to foresee such errors their responsibility for them will increase Safety at the Group Level There are two organizations at this level whose actions need to be thought about the treatment facilities and Atomic Energy Canada Limited Atomic Energy Canada Limited With regard to safety in this case AECL s responsibility in making a medical linear accelerator are to a range of individuals their shareholders their employees the governments of Canada and the United States to the facilities that bought the machine and finally to the patients who were treated by them Responsibility to shareholders and employees are similar and for this analysis will be considered the same Before we look at these specific responsibilities we will need to understand some of the technical issues involved in the analysis of a system for safety In this instance technical knowledge is required to make ethical judgments AECL claimed to do a safety analysis of its machine but in fact the analysis only shows the likelihood of the system failing because a part wears out There was apparently no systematic search for design flaws in the software until after the FDA required an analysis Unfortunately a system can be highly reliable but thereby reliably kill people because of a design flaw This confusion of reliability analysis and safety analysis is a critical failing on the part of AECL Some indication of the motivations behind AECL s inadequate safety analyses can be gleaned from the way AECL appeared to use probabilities in its analysis These probabilities seemed to be assigned to quantify and to prove the safety of the system rather than to identify design flaws For example after redesigning the logic to track the microswitches that indicated the position of the turntable AECL apparently used a sort of Fault Tree Analysis to assert that the safety of the system had been improved by at least 5 orders of magnitude This astonishing claim of improvement is applied to the safety of the entire machine This use of probabilities from a Fault Tree Analysis can effectively hide critical design flaws by inflating the perception of reliability and discouraging additional search for design flaws This hiding of design flaws was a tragic if unintentional side effect of the improper use of this analysis Thus in failing to look systematically for design flaws in its software AECL left itself and its employees and shareholders open to liability claims from injured consumers This is clearly also a failure of its responsibility to patients and to the facilities who bought the Therac 25 machine and who were assured there was no way it could hurt

    Original URL path: http://computingcases.org/case_materials/therac/analysis/Safety.html (2016-04-30)
    Open archived version from archive

  • Property
    proprietary rights to the software and would not make it public This is another case of two values coming into conflict A concern for safety suggests that it would be helpful to open the source code to inspection by the FDA or its agents or by the user groups But to force this openness would violate the property rights of the owner of the software AECL One suspects that AECL s refusal to open the code to inspection is a defensive move based on avoiding liability rather than an attempt to protect the value of the intellectual property But if close inspection showed the software to be poorly designed the value of the software would surely diminish Is this a case in which we want to uphold property rights There may in fact be some case here for an open software standard to protect public safety The ImpactCS grid suggests we identify several levels of social analysis for each ethical issue In this case we have interaction among those levels The public ideally represented by the FDA was placed at great risk by the software What claims are there that the cancer treatment facilities and the FDA can make regarding

    Original URL path: http://computingcases.org/case_materials/therac/analysis/Property.html (2016-04-30)
    Open archived version from archive



  •