Software Bugs in Medicine

“01110011 01101111 01100110 01110100 01110111 01100001 01110010 01100101 00100000 01100010 01110101 01100111 01110011.” Translation: “Software Bugs”

Some fields in medicine are heavily dependent on technological innovation. Radiation oncology is one. Radiation therapy is highly effective in some cancer treatments. From cures to palliative treatments, millions of people are better off because of the innovation. As we move forward in medicine with further technological change, It is essential to look back remind ourselves of the failures. 



The Therac-25 was a radiation therapy machine used in the 1980s to treat cancers. Unfortunately, programming errors caused massive overdoses of radiation, leading to patient harm and sometimes death. In an age where software controls cars, planes, and medical devices, it is essential to remember our mistakes. 


The Accidents (written by Anne Marie Porrello)


Six accidents involving enormous radiation overdoses to patients took place between 1985 and 1987.

The first accident occurred at Kennestone Regional Oncology Center in Marietta. On June 3, 1985, a sixty-one year old woman was receiving follow-up treatment after a malignant tumor was removed from her breast. When the machine was activated, she felt "a tremendous rush of heat&ldots;this red-hot sensation." She told the operator of the Therac-25 "you burned me." Although later she developed reddening and swelling in the center of the treatment area, AECL denied that the machine burned the patient. and the swelling was attributed to normal treatment reaction. Eventually, her shoulder froze and she began to experience spasms. She was admitted to the hospital, but her doctors continued to send her for Therac-25 radiation treatments. Eventually the patient's breast had to be removed, and she completely lost the use of her shoulder and arm (Leveson and Turner, 1993, p. 22).

The second accident occurred at the Ontario Cancer Foundation clinic in Canada. On 26 July 1985, a 40-year old patient received her 24th Therac-25 treatment. During the treatment, the machine caused a treatment pause and issued an "H-tilt" error message. The operator proceeded to push the "P" button since the machine indicated that no dose had been delivered to the patient. The machine continued to shut down and the operator pushed the "P" button each time until the machine suspended after the fifth attempt. Each time the machine indicated that no dose had been given to the patient. The operator of the Therac-25 was used to this type of behavior from the machine and called the technician, who found nothing wrong with the machine. This also was a common situation. The patient, however, complained of an "electric tingling shock" in her hip. Eventually radiation overexposure was suspected and the patient was hospitalized. She died three months later of cancer, but a total hip-replacement would have been necessary if she had continued to live (Leveson and Turner, 1993, p. 23) .

The third accident involved a woman who developed red parallel stripes on her hip, the treatment area. She was treated at the Yakima Valley Memorial Hospital in 1985. Her doctors continue to order treatments for her even after these stripes appeared. Radiation overexposure was not considered as a cause until over a year later. Eventually, the patient received surgical treatment and, except for minor disability and scarring, is alive and well today (Leveson and Turner, 1993, p. 26-27).

Another Therac-25 accident, the fourth in the series, developed at the East Texas Cancer Center in March of 1986. A male patient was to receive therapy on his upper back. The Therac-25 operator had typed in incorrect treatment information by indicating X-ray mode instead of electron mode. She merely used the "cursor up" key to edit the mode entry and then quickly pressed "enter" (one of the user-friendly features), and started treatment. The machine shut down with treatment pause, and a "malfunction 54" error message was displayed on the screen. This error message indicated that either a dose too high or a dose too low had been delivered. Since an underdose value appeared on the screen and the operator was used to quirks in the machine, she hit the "P" key to continue with the treatment. The machine repeated the "Malfunction 54" error message and indicated the same underdose was delivered. The operator had no contact with the patient, because the usual audio and video monitors were not working properly. After the first attempt at treatment, the patient felt an "electric shock" or as if "someone had poured hot coffee" on his back. He knew this was not normal and began to get up from the treatment table when the second treatment was delivered. The patient felt a tremendous shock in his arm, and felt that "his hand was leaving his body". He had to pound on the treatment room door to get the operator's attention. The patient eventually loss the use of his left arm and both legs, was unable to speak, and had several other complications. He died from complications five months later (Leveson and Turner, 1993, p. 27-28).

A fifth accident occurred, the second at the East Texas Cancer Center, in April of 1986, just one month later. As in the previous accident, the same operator entered the wrong mode of treatment and quickly edited the correct mode in and hit a quick serious of enter keys. The machine shut down again with a "Malfunction 54" message. This time, however, the intercom had been working and the operator heard a loud noise followed by moaning from the patient. The patient was receiving radiation on the side of his face. He died three weeks after the accident, after falling into a coma and suffering severe neurological damage (Leveson and Turner, 1993, p. 28) .

The last of the accidents occurred at the Yakima Valley Memorial Hospital. On January 17, 1987 an operator placed a patient on the turntable in the field-light position for small position verification doses. After attempting to administer the treatment dose, the machine shut down with a quick malfunction message and a treatment pause. The operator pushed the "P" button, and the machine paused again. The machine indicated that the patient had received his prescribed 7 rad of treatment. The patient, however, complained of a "burning sensation" and died three months later from complications related to the overdose (Leveson and Turner, 1993, p. 33) .


Unfortunately, this is only one example of how software caused harm. Only one-third of one percent of people in the world understand code or coding languages. Physicians use many of these tools without checking or understanding the "code." We should take ownership of the oath we took, "First, Do No Harm."

Cesar O. Avila, M.D. FACEP