Java Reference
In-Depth Information
Therac-25
What Happened?
The Therac-25 was a radiation therapy
machine used to deliver targeted elec-
tron or X-ray beams in order to destroy
cancerous tissue. While in use, hundreds
of patients were given proper treatments
using this device. But in six documented
cases from 1985 to 1987, the Therac-25
delivered an overdose of radiation result-
ing in severe disability and death.
In a typical treatment, the patient lies
down and the operator adjusts the
machine to target the appropriate area of
the body. The operator sets the param-
eters of the treatment on the machine's
computer console and pushes a button
to deliver the radiation. Patients are told
that a typical side effect is minor skin dis-
comfort similar to that of a mild sunburn.
In the accident cases, some patients
reported feeling a “tremendous force of
heat” or an “electric tingling shock.” In
one case, the patient lost the use of her
shoulder and arm and had to have her left
breast removed because of the radiation
damage. Several others died of radiation
poisoning.
The amount of radiation delivered is
measured in rads (radiation absorbed
dose). A standard treatment is around
200 rads. It's estimated that the accidents
caused 20,000 rads to be administered.
■
Radiation therapy
machines deliver
precise amounts of
targeted radiation.
What Caused It?
The operators were told the Therac-25 had so many safety precautions that it
would be “virtually impossible” to overdose a patient. But part of the software
used in the Therac-25 was reused from an earlier version of the machine that had
included many hardware-based safety precautions. Thus, the hardware features
267
Search WWH ::
Custom Search