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THERAC-25 A MEDICAL ENGINEER DISASTER
-Therac-25 was a computer-controlled radiation therapy machine designed by Atomic Energy of Canada Limited and a French company by the name of CGR. -It was a particle accelerator built upon the prior Therac-6 and Therac-20 models. -Could deliver both electron beam and x-ray beam therapy to treat tumors. Accelerated electrons were used to treat tumors in more shallow tissues (such as the skin), while deeper tissues were targeted by x-ray. -
FDA APPROVAL OF THERAC-25
-Therac-25 was released on the market. -AECL performed a safety analysis, but this excluded the analysis of the software. -AECL received approval by the FDA and the machine became commercially available. -FDA approved the Therac-25 on "pre-market" equivalence. The software of the machine was based on software that was already in use, and the linear accelerator was a minor modification of previous technology; this meant that the Therac-25 by-passed the rigorous testing procedures of the FDA. -
RADIATION ABSORBED DOSE
-Malfunctions of Therac-25 will result in massive radiation overdoses, resulting in 4 patient deaths and 2 others with lifelong injuries. -Rad is used to measure the beam in radiation therapy. Single standard radiation treatments are in range of 200 rad. -The unprotected electron beam in the Therac-25 was capable of producing 15,000 and 20,000 rads in a single treatment; which should never be pointed at the patient. -
1st Incident Kennestone Regional Oncology Center Marietta, Georgia
-Patient set to receive 10 meV to her clavicle following a lumpectomy. -During therapy she complained of a tremendous force of heat and hot sensation. The technician stated it wasn't possible.- This was treated as a symptom of her cancer, but the hospital physicist later calculated her absorbed dose to be between 15,000 and 20,000 rad, when she should have been dosed with 200 rad.
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2nd Incident Ontario Cancer Foundation
-Patient underwent her 24th treatment for cervical cancer. -When the operator activated treatment, The machine stopped after 5 seconds with an error message. The dosimeter and halt of the system indicated that no radiation had been applied. -The operator continued the treatment 5 times until the machine finally stopped the treatment. A technician was called, and they found no problem. -AECL is informed of the incident and sends a service engineer to investigate. -
2nd Incident Ontario Cancer Foundation Contn'd..
-The patient complained of burning and swelling in the area treated and was hospitalized on July 30th. -Patient was suspected of radiation overdose, and the machine was taken out of service. -November 3rd, 1985 the patient died of cancer, but if the patient had not died an autopsy stated that she would have needed a hip replacement due to the radiation damage. -The incident was reported to the FDA and Canadian Radiation Protection Bureau. -Estimated absorbed dose was 13,000-17,000 rad. -
AECL Response to Marietta, Georgia Incident
-AECL heard of another incident in Georgia. The patient had filed suit that month based on an overdose that occurred in June. -There was no evidence that AECL followed up this case with the Georgia hospital. This information was clearly received by AECL, but there is no evidence that this information, was communicated internally to engineers or others who responded to later accidents. -
3rd Incident Yakima Valley Memorial Hospital Yakima,Washington
-A woman developed erythema with a parallel band pattern after receiving treatment. -6 months later the patient developed chronic ulcers under the skin due to tissue necrosis. The patient had surgery and skin grafts, but continued to live with minor sequelae.- January 31st, 1986 the hospital sent a letter to AECL about the incident.
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AECL Response To 3rd Incident In Yakima, Washington
-In January 1986 AECL heard from the hospital in Yakima, Washington that a patient had been overdosed. -The AECL technical support supervisor spoke with the Yakima hospital staff on the phone and contacted them by letter indicating that they did not think the damage they reported was caused by the Therac-25 machine. -AECL notified hospital that there have "apparently been no other instances of similar damage to this or other patients." -
4th Incident East Texas Cancer Center Tyler, Texas Cont'd
-The machine stopped and read an error message detailing "Malfunction 54" and "dose input 2" which indicated that the dose was too high or too low. -The patient began to feel electric shocks through their arm. -Intense erythema was observed in the area after a physician was called. Suspecting that the patient had simply experienced electric shock, the patient was sent home. -
4th Incident East Texas Cancer Center Tyler, Texas
-Patient came in for their 9th treatment of a tumor on their back. Treatment was set to be 22 MeV of electrons with a dose of 120 rad with an accumulated dose of 6000 rad in the course of 6 weeks. -The operator realized that she had written down "x" for x-ray instead of "e" for electron beam as the type of therapy the patient was to receive; the operator changed x-ray to e- beam. -All parameters were verified; the machine read "rays ready" and the operator selected beam on. -
4th Incident East Texas Cancer Center Tyler, Texas Cont'd
-Patient checks into the hospital experiencing paralysis of the left arm, nausea, vomiting, and hospitalized for radiation induced myelitis. Legs, vocal cords and mid-diaphragm paralyzed; Patient died 5 months after the overdose. -Patient received 16,500-25,000 rads in less than 1 sec. -The crackling of the machine had been produced by saturation of the ionization chambers. -
AECL Response To 4th Incident Tyler, Texas
-The AECL engineer suggested that perhaps an electrical problem had caused the accident. -AECL engineers checked the machine and were unable to replicate error 54. They checked the grounding of the machine to rule out electric shock as the cause. -An independent engineering firm checked out the electric shock theory and found that the machine did not seem capable of delivering an electric shock to a patient. -The machine was back in operation on April 7, 1986. -
5th Incident East Texas Cancer Center Tyler, Texas
-Patient received electron therapy treatment for skin cancer of the face. -The machine produced a loud noise once therapy began which caused the operator to enter the room; "Error 54" displayed on the monitor, and patient described a burning sensation to the face. -The patient died May 1st, 1986. Their autopsy showed severe radiation damage to their right temporal lobe and brainstem. -AECL unable to replicate error message, although hospital physicist and operator were able to. -
AECL Response To 5th Incident/FDA Interference
-AECL files report with FDA. -FDA declared Therac-25 defective and ordered the AECL to contact all sites that used the machine, investigate the problem, and submit a report called a corrective action plan. -AECL contacted all sites and recommended a temporary fix involving removing some keys from the keyboard at the computer console. -
AECL Response To 5th Incident/FDA Interference Cont'd
-The FDA was not satisfied with the notification that AECL gave sites, and in May 1986 required AECL to re-notify all sites with more information about the defect in the product and the hazards associated with it. -AECL involved in meetings with a "user's group" of Therac-25 sites to help formulate its corrective action plan. -After several exchanges of information between AECL and FDA December 1986, AECL submitted a revised corrective action plan to FDA. -
6th Incident Yakima Valley Memorial Hospital Yakima, Washington Cont'd
-Monitor showed that patient had only received 7 rad. -Hospital physicist conducted tests with film plates since they were used for the patients' treatment, to see if they could reproduce the incident. It was found patient had been exposed to 8,000 and 10,000 rad instead of 86 rad; AECL was unable to reproduce the event. -Patient died April 1987 from complications due to radiation overdose. -
6th Incident Yakima Valley Memorial Hospital Yakima, Washington
-Patient was to receive 2 film verification exposures of 3-4 rad and a 79 rad photon treatment for a total exposure of 86 rads. -Operator completed films, changed patient position, and began beam on therapy. After 5 seconds the machine stopped; operator pressed "proceed". The machine stopped again showing "flatness" as the reason. -Operator heard the patient on intercom, couldn't make out what was said. Patient felt severe burning in chest; hours later patient showed skin burns in the area. -
AECL To 6th Incident Yakima,Washington
-AECL was notified of another overdose occurring again at the Yakima, Washington hospital. -AECL sent an engineer to investigate this incident. -AECL concluded that there was a different software problem that allowed the electron beam to be turned on without the device that spread it to a safe concentration being placed in the beam. -
THERAC-25 Shut Down
-FDA and Canadian counterpart cooperated to require all units of Therac-25 to be shut down. -After 6 months of negotiation with the FDA, AECL received approval of final corrective action plan. Plan included software fixes, installation of independent mechanical safety interlocks and other safety changes. -Therac-25 is still shut down to date. -Surviving victims or the deceased victim’s families filed suit against AECL/medical facilities using Therac-25. Suits were settled out of court.