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en:passport:therac-25

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en:passport:therac-25 [2026/07/16 11:11] – Automatic translation vamsanen:passport:therac-25 [2026/07/16 21:56] (current) – vamsan
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 First, the radiology technician positioned the patient on the treatment table and manually adjusted the machine’s gantry and the size of the irradiation field, as well as securing the necessary accessories. By setting the machine to ‘field light’ mode, a visible light was projected onto the patient using a mirror. This showed exactly where the (ideally) invisible beam would be directed. First, the radiology technician positioned the patient on the treatment table and manually adjusted the machine’s gantry and the size of the irradiation field, as well as securing the necessary accessories. By setting the machine to ‘field light’ mode, a visible light was projected onto the patient using a mirror. This showed exactly where the (ideally) invisible beam would be directed.
  
-The technician then left the shielded room and, using the external terminal (keyboard and monitor), entered the patient’s details and the treatment plan: the operating mode (electron or X-ray), the energy level and the dose. The software compared the data entered at the terminal with the machine’s mechanical settings. If they matched, the //"VERIFIED"// message appeared. Finally, the  technician pressed the //"Beam ON"// button to start the treatment, which usually lasted 1–5 minutes. +The technician then left the shielded room and, using the external terminal (keyboard and monitor), entered the patient’s details and the treatment plan: the operating mode (electron or X-ray), the energy level and the dose. The software compared the data entered at the terminal with the machine’s mechanical settings. If they matched, the //"VERIFIED"// message appeared. Finally, the technician pressed the //"Beam ON"// button to start the treatment, which usually lasted 1–5 minutes. 
  
 ===== The fateful “speed” ===== ===== The fateful “speed” =====
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 When the **Malfunction 54** appeared, the machine did not shut down in an emergency; instead, it merely //‘paused’// (Pause) the treatment. The operating staff understood that faults causing a pause were harmless (such as a minor voltage fluctuation), and that the procedure could simply be resumed by pressing the  "P" (Proceed) button. When the **Malfunction 54** appeared, the machine did not shut down in an emergency; instead, it merely //‘paused’// (Pause) the treatment. The operating staff understood that faults causing a pause were harmless (such as a minor voltage fluctuation), and that the procedure could simply be resumed by pressing the  "P" (Proceed) button.
  
-Next to the fault on the screen, the message //‘No dose’// (no dose), meaning the machine indicated that it had not yet delivered any radiation at all. The operator therefore pressed the ‘Proceed’ button with a clear conscience, so that the patient would receive the planned dose – whilst in reality, with every single press of the button, the machine was performing another lethal release of the safety latch.+Next to the fault on the screen, the message //‘No dose’// (no dose), meaning the machine indicated that it had not yet delivered any radiation at all. The operator therefore pressed the ‘Proceed’ button with a clear conscience, so that the patient would receive the planned dose, whilst in reality, with every single press of the button, the machine was performing another lethal release of the safety latch.
  
 The technicians saw as many as 40 similar error messages a day, most of which were indeed harmless. As a result, they developed a sort of //‘alarm fatigue’//: they viewed Malfunction 54 as just one of many annoying but insignificant software glitches. The technicians saw as many as 40 similar error messages a day, most of which were indeed harmless. As a result, they developed a sort of //‘alarm fatigue’//: they viewed Malfunction 54 as just one of many annoying but insignificant software glitches.
  
-On several occasions, patients reported after their treatments that something was wrong. Ray Cox, one of the victims, described an //“electric shock”// and saw a bluish light flashing from the machine. However, the hospital staff did not believe them at first, as the monitor indicated that everything was proceeding perfectly normally.+On several occasions, patients reported after their treatments that something was wrong. Ray Cox, one of the victims, described an //“electric shock”// and saw a bluish light flashing from the machine. However, the hospital staff did not believe them at first, as the monitor indicated that everything was proceeding normally.
  
 When the hospital in Tyler first reported the problem to AECL, the manufacturer responded (rather arrogantly) by stating that there had never been a case of radiation overdose with the Therac-25. They claimed that the machine was safe in terms of both hardware and software, and attributed the fault to an electrical short circuit, but primarily to human error.  When the hospital in Tyler first reported the problem to AECL, the manufacturer responded (rather arrogantly) by stating that there had never been a case of radiation overdose with the Therac-25. They claimed that the machine was safe in terms of both hardware and software, and attributed the fault to an electrical short circuit, but primarily to human error. 
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 ===== Fritz Hager’s private investigation ===== ===== Fritz Hager’s private investigation =====
-**Fritz Hager**, who works at the **East Texas Cancer Centre** , did not accept the manufacturer’s explanations. When, in April 1986, a second patient observed the same highly suspicious phenomena with the same technician, Hager resolved not to stop testing the machine until he had reproduced the phenomenon.+**Fritz Hager**, who works at the **East Texas Cancer Centre**, did not accept the manufacturer’s explanations. When, in April 1986, a second patient observed the same highly suspicious phenomena with the same technician, Hager resolved not to stop testing the machine until he had reproduced the phenomenon.
  
 Hager and the technician spent hours and days trying out the machine, but it operated without fault. Eventually, they discovered the secret: the technician had to type as quickly as he usually did during his daily routine. When Hager managed to carry out the repair within 8 seconds, the machine finally displayed the infamous **‘Malfunction 54’** message. Hager and the technician spent hours and days trying out the machine, but it operated without fault. Eventually, they discovered the secret: the technician had to type as quickly as he usually did during his daily routine. When Hager managed to carry out the repair within 8 seconds, the machine finally displayed the infamous **‘Malfunction 54’** message.
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 Finally, during the investigation, it was analysed that the **PDP-11 computer** was running a real-time operating system that handled multiple tasks (tasks) simultaneously. In the software, processing data from the keyboard and physically adjusting the machine (such as rotating the disc) were two separate processes.  Finally, during the investigation, it was analysed that the **PDP-11 computer** was running a real-time operating system that handled multiple tasks (tasks) simultaneously. In the software, processing data from the keyboard and physically adjusting the machine (such as rotating the disc) were two separate processes. 
  
-When the operator switched from X-ray mode to Electron mode, the software initiated a process to move the dial. However, if the operator made the correction within 8 seconds, part of the software had already recognised the new data, but the part responsible for the machine’s physical settings was still operating in the old state.  The machine believed everything was ready, but in fact it emitted the enormous amount of radiation required for X-ray mode onto the patient.+When the operator switched from X-ray mode to Electron mode, the software initiated a process to move the dial. However, if the operator made the correction within 8 seconds, part of the software had already recognised the new data, but the part responsible for the machine’s physical settings was still operating in the old state.  The machine believed everything was ready, but in fact, it emitted an enormous amount of radiation required for X-ray mode onto the patient.
  
 ===== Consequences =====The Therac-25 tragedy fundamentally shook the foundations of medical device regulation and the ethics of software development. ===== Consequences =====The Therac-25 tragedy fundamentally shook the foundations of medical device regulation and the ethics of software development.
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 In 1987, the US Food and Drug Administration (FDA) declared the equipment to be defective and ordered all Therac-25 machines to be taken out of service until the manufacturer had carried out the necessary modifications. In 1987, the US Food and Drug Administration (FDA) declared the equipment to be defective and ordered all Therac-25 machines to be taken out of service until the manufacturer had carried out the necessary modifications.
  
-More than 20 modifications were eventually made to the machines, including the installation of mechanical safety interlocks – which had previously been omitted – capable of stopping the radiation independently of the software.  Following the incident, hospitals were required to report all serious accidents to the authorities. Previously, manufacturers had been able to conceal faults, meaning that different hospitals were unaware of incidents at other hospitals. +More than 20 modifications were eventually made to the machines, including the installation of mechanical safety interlocks, which had previously been omitted, capable of stopping the radiation independently of the software.  Following the incident, hospitals were required to report all serious accidents to the authorities. Previously, manufacturers had been able to conceal faults, meaning that different hospitals were unaware of incidents at other hospitals. 
  
 [{{ passport:therac_25_3.png |Therac-25 diagram, Source: createdigital.org.au / Diagram adapted from Leveson (1995)}}] [{{ passport:therac_25_3.png |Therac-25 diagram, Source: createdigital.org.au / Diagram adapted from Leveson (1995)}}]
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 In a recent publication, he stated that the Therac-25 incidents are unique in the history of radiotherapy, and that it is important for these //“are learnt in the classroom, rather than at the cost of human lives”//. Without the physicist’s determination, there would likely have been even more victims of the faulty software, as the manufacturer (AECL) denied all allegations in the face of his overwhelming evidence.  In a recent publication, he stated that the Therac-25 incidents are unique in the history of radiotherapy, and that it is important for these //“are learnt in the classroom, rather than at the cost of human lives”//. Without the physicist’s determination, there would likely have been even more victims of the faulty software, as the manufacturer (AECL) denied all allegations in the face of his overwhelming evidence. 
  
-{{page>passport:great_bugs}}+{{page>en:passport:utolso_bejegyzesek}}
  
-{{page>passport:lablec}}+{{page>en:passport:lablec}}
  
 ===== Sources ===== ===== Sources =====
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 [[https://ethicsunwrapped.utexas.edu/case-study/therac-25|ethicsunwrapped.utexas.edu - Therac-25]] \\  [[https://ethicsunwrapped.utexas.edu/case-study/therac-25|ethicsunwrapped.utexas.edu - Therac-25]] \\ 
 [[https://w3.cs.jmu.edu/lam2mo/papers/2004-JMU-Therac.pdf|w3.cs.jmu.edu - 2004-JMU-Therac.pdf]]\\  [[https://w3.cs.jmu.edu/lam2mo/papers/2004-JMU-Therac.pdf|w3.cs.jmu.edu - 2004-JMU-Therac.pdf]]\\ 
-===== Recommended by ===== 
-Similar posts can be found at **‘Interesting Stories’** section: {{topic>erdekes_toertenet&nodate&nouser}} 
  
-{{tag>2026 Therac-25 great_bugs lineáris_gyorsító linac 1980 AECL Malfunction_54 Fritz_Hager FDA PDP-11 erdekes_toertenet tech USA}}+{{tag>2026 Therac-25 great_bugs linear_accelerator linac 1980 AECL Malfunction_54 Fritz_Hager FDA PDP-11 interesting_history tech USA}}
  
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en/passport/therac-25.txt · Last modified: by vamsan