The Therac-25 Radiation Therapy Machine

Canadian Atomic Energy Co., Ltd. (AECL) has created a Therac-25 radiation therapy machine (death and rejection). The main technological innovation of this machine is that it is more computer controlled than its predecessor. This allows the technician to shorten the time spent setting up the machine and increase the time to work directly with the patient. Patients treated with Therac - 25 communicate with machine operators (in separate rooms) via AV monitors (death and rejection).

There is a serious error in the security software of Therac-25 device, which causes the high current electron beam to hit the patient with the expected radiation dose of about 100 times, and potentially lethal doses of beta radiation in the narrower area provide. A strong electric shock made them scream and ran out of the room. A few days later, radiation burns occurred and the patient began to develop symptoms of radioactive poisoning. This is due to an error in Therac-25 machine programming. If the operator switches between two modes, direct beam therapy mode and Megavolt X-ray therapy mode quickly, the security software encounters a race condition, enters a deadlock and can not decide how to deal with it. Then it shows the behavior of undocumented code called a bug

A radiotherapy machine was built around the 80 th company. It is the second or third radiotherapy machine produced by the company. There are two modes of operation in this machine: low radiation mode and high radiation mode. Only the first model can be used by humans. The second mode is just a service mode (for example for calibration). After investigating these events, I found that it was a minor programmer's mistake. Yes, this is a small bug in this machine program. The company's programmer did not correctly check the state of the current mode (low or high radiation). High radiation mode may turn on automatically during treatment. The salary of this package is the lives of many people.