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  • Linear Accelerator Treatment Facility
    paperwork janitorial staff etc are required Machine Support and Maintenance Medical Linear Accelerators do age over time and older machines often produce more errors Five to ten years is a reasonable life span for a machine Thus simply to maintain a set of three medical linear accelerators an institution can expect to spend 1 to 2 million dollars every third year Sometimes errors can be resolved and machine kept longer using software upgrades or upgrades or retrofits of machine parts The companies that sell linear accelerators charge maintenance contracts that can include different levels of support Because of monetary constraints sometimes facilities are forced to choose between software updates manuals and training for operators and physicists All this is in addition to the price of the machine itself Production Pressures Production pressures are always present when an expensive medical technology is being used These very expensive machines need to treat enough patients to pay for themselves over their lifetime And in for profit medical facilities the additional pressure of generating a profit is added to this production pressure Another kind of production pressure is generated because of concern for the patient Patients schedules require treatments on certain days and it disrupts the patients lives and slows down their treatment to have to reschedule them for another day while the machine is being checked out These production pressures generate the desire to push patients through If a machine gives only a portion of the prescribed dose an operator will often repeat the treatment with enough radiation to add up to the total prescribed dose Of course because of liability issues and concerns for patient welfare this can only be done when it is thought safe One of the advantages of the significant computerization of the Therac 25 machine was that setup

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/Hospital.html (2016-04-30)
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  • FDA
    require performance standards in addition to general controls Class III devices like heart valves and pacemakers are required to undergo pre market approval as well as complying with general controls In addition to classifying devices as Class I II or III FDA approved devices for market in one of two ways Proof of Pre market Equivalence to another device on the market termed 501 k OR Pre market Approval Rigorous Testing If a company could show Pre market Equivalence proof that a new product was equivalent to one already on the market the new product could be approved by FDA without extensive costly rigorous testing In 1984 about 94 of medical devices came to market through Pre market Equivalence If a product was not equivalent to one that was already on the market FDA required that the product go through testing to gain Pre market Approval In 1984 only about 6 of medical devices were required to go through this testing Thus it was clearly in the interest of medical device producers to show that their product had pre market equivalence The Therac 25 brought to market in 1983 was classified as a Class II medical device Since Canadian Medical Company AECL designed the Therac 25 software based on software used in the earlier Therac 20 and Therac 6 models Therac 25 was approved by FDA under Pre market Equivalency Medical Error Reporting and FDA Reporting Requirements A 1983 General Accounting Office GAO report criticized the FDA s adverse experience warning system as inadequate FDA had published reports about potential hazards including reports in their own newsletter The FDA Consumer The FDA implemented the mandatory medical device reporting rule after Congress passed the Medical Device Reporting Legislation in 1984 This rule required manufacturers to report injuries and problems that could

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/fda.html (2016-04-30)
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  • Linear Accelerator Operators
    edit the parameters at the console without having to start all over again from inside the treatment room When the computer indicates that the setup has been done correctly the operator presses the actuation switch The computer turns the beam on and the treatment begins When treatment is over the operator checks with the patient updates records on that patient and then admits the next patient into the treatment room One of the advantages of the significant computerization of the Therac 25 machine was that setup for treatment could be done much more quickly This allowed the operator more time to speak with the patient and interact with them about their health concerns In addition this increased efficiency allowed more patients to be scheduled during a day Thus more patients could be treated but the atmosphere was not reduced to that of a factory Dealing with difficulties If a treatment resulted in a suspend or cancellation by the machine the operator had several choices For some machine errors the operator could simply press the retry button and attempt the therapy over again If only half the prescribed dose had been introduced e g the beam was a lower intensity or cut off early the rest of the dose might be applied in a second immediate treatment If the error was more significant many hospitals and facilities would have a medical physicist on call The physicist could be called in to look at the machine immediately For facilities without a full time physicist contract service was usually provided This required scheduling but usually within the same day as the problem All errors whether by the machine or by the operator were supposed to be logged and reported Medical Linear Accelerators do age over time and older machines often produce more errors Five to ten years is a reasonable life span for a machine Close tracking of these errors by operators allows the hospital or facility to know when to replace a machine that is generating more errors than is acceptable Even if errors are not harmful to patients when a treatment must be restarted several times it may reduce patient confidence in the facility Pressures for Production Production pressures are always present when an expensive medical technology is being used Machines need to treat enough patients to pay for themselves over their lifetime And in for profit medical facilities the additional pressure of generating a profit is added to this production pressure Another kind of production pressure is generated because of concern for the patient Patient schedule requires treatments on certain days and it disrupts the patients lives and slows down their treatment to have to reschedule them for another day while the machine is being checked out These production pressures generate the desire to push patients through If a machine gives only a portion of the prescribed dose an operator will often repeat the treatment with enough radiation to add up to the total prescribed dose Sometime this repeat has

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/Operators.html (2016-04-30)
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  • Canadian Medical Company
    beam producing mechanism for a 25 MeV machine into a smaller space In addition this new version was somewhat less expensive to produce since it used a less expensive beam production device a magnetron instead of a klystron Finally AECL intended to take advantage of increasing capability of computer software to make the machine easier to operate The new Therac 25 was the result of a convergence of the new beam folding technology with the ease of computer control bringing with it the bonus of lower production costs In addition to lower production costs the computer control allowed faster setup of the machine for each patient This meant that more patients could be treated in one day than with non computerized linear accelerators The Therac 25 s ancestors Therac 20 and Therac 6 had used a minicomputer a DEC PDP 11 to add some convenience to the standard hardware of a medical linear accelerator They both could work without computer control AECL determined to make its new model Therac 25 a tightly coupled combination of software and hardware By this time its collaboration with CGR had grown stale and AECL was bringing in its new beam folding technology and the new Therac 25 on its own In tightly coupling the software and the hardware AECL could use the software to monitor the state of the machine for proper operation and for safety Previous versions with designs based in models that predated computer control had included independent circuits to monitor beam scanning and had mechanical interlocks to ensure the machine could not enter a state in which it could harm a patient But with increased computer control AECL decided not to duplicate this equipment in the Therac 25 with some cost savings and to rely on software for policing these safety

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/cmc.html (2016-04-30)
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  • Linda Knight Accident Account
    heat this red hot sensation When the technician re entered the therapy room Knight said you burned me The technician replied that that was not possible Back home the skin above Knight s left breast began swelling The pain was so great that she checked in at Atlanta s West Paces Ferry Hospital a few days after the Therac incident For a week doctors at West Paces Ferry continued to send Knight back to Kennestone for Therac treatment but when the welt on her chest began to break down and lose layers of skin Knight refused to undergo any more radiation treatment About two weeks later the physicist at Kennestone noticed that Knight had a matching burn on her back as though the burn had gone through her body The swelling on her back had also begun to slough off skin Knight was in great pain and her shoulder had become immobile These clues led the physicist to conclude that Knight had indeed suffered a major radiation burn Knight had probably received one or two radiation doses in the 20 000 rad radiation absorbed dose range well above the typical prescribed dosage of around 200 rads The physicist called AECL

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/linda_knight.html (2016-04-30)
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  • Donna Gartner Accident Accounts
    day without any incidents However despite the fact that the Therac had indicated that no radiation dose had been given during Donna Gartner s five therapy attempts that day Gartner complained of a burning sensation she described as an electric tingling shock in the treated area of her hip Gartner returned for treatment three days later on July 29 and was hospitalized for suspected radiation overexposure She had considerable burning pain and swelling in the treatment region of her hip The Hamilton clinic took the Therac 25 machine out of service and informed AECL of the incident This was the first time AECL had heard from a clinic about an overdose problem with the Therac 25 machine AECL sent a service engineer to investigate AECL reported to a range of stakeholders that there was a problem with the operation of Therac 25 The FDA the Canadian Radiation Protection Board the parallel Canadian agency to the FDA and other Therac 25 users were all notified Users were instructed to visually confirm that the Therac turntable was in the correct position for each use Because of the Hamilton accident AECL issued a voluntary recall of the Therac 25 machines and the FDA

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/donna_gartner.html (2016-04-30)
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  • Janis Tilman Accident Accounts
    an abnormal reaction Hospital staff monitored the skin reaction and searched unsuccessfully for possible causes for the striped marks The hospital sent a letter to AECL and spoke on the phone with AECL s technical support supervisor who later sent a written response stating After careful consideration we are of the opinion that this damage could not have been produced by any malfunction of the Therac 25 or by any

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/janis_tilman.html (2016-04-30)
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  • Isaac Dahl Accident Accounts
    monitor The machine indicated that only 6 of the prescribed 202 units of radiation had been delivered The screen of the console showed that this shut down was a treatment pause which indicated a problem of low priority since little radiation had been delivered The operator hit the P key to proceed with the therapy but after a moment of activity Malfunction 54 appeared on the Therac control screen again The operator was isolated from Dahl because the Therac 25 operates from within a shielded room On this day at the ETCC the video monitor was unplugged and the audio monitor was broken leaving no way for the operator to know what was happening inside Isaac Dahl had been lying on the treatment table waiting for the usually uneventful radiation therapy when he saw a bright flash of light heard a frying buzzing sound and felt a thump and heat like an electric shock Dahl knowing from his previous 8 sessions that this was not normal began to get up from the treatment table when the second attempt at treatment occurred This time the electric like jolt hit him in the neck and shoulder He rolled off the table and pounded on the treatment room door until the surprised Therac 25 operator opened it Dahl was immediately examined by a physician who observed reddening of the skin but suspected only an electric shock Dahl was discharged and told to return if he suffered any further complications The hospital physicist was called in to examine the Therac 25 but no problems were found The Therac 25 was shut down for testing the next day and two AECL engineers one from Texas and one from the home office in Canada spent a day at the ETCC running tests on the machine but

    Original URL path: http://computingcases.org/case_materials/therac/supporting_docs/therac_case_narr/isaac_dahl.html (2016-04-30)
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