There was another incident too. About 15 years after the Therac-25 incident in November 2000 at the National Cancer Institute in Panama twenty-eight patients were exposed to dangerous levels of radiation due to a series of faulty calculations caused by a lack of proper software testing.
The Cobalt-60 machine in Panama was overused and under maintained due to a lack of proper funding as well as understaffing issues. For this reason, some of the physicists were motivated to test a new method on how to align the shields in the hopes of not only making the entire process easier but also providing extra protection for their patients. Instead of applying the usual four blocks, they implemented a fifth one with no objections from the software or the accompanying manual and noticed that they were even able to create composite shapes, such as a rectangle with triangles in each corner, in the 3D pictures of the shields.
However, what they didn’t expect was that the addition of the extra block as well as the fact that the software was unable to accurately recognize the shapes would lead to a miscalculation of treatment times. Therefore, depending on the amount of treatments a patient received, they were subjected to radiation levels 20 to 100% more than the prescribed dose putting them well into dangerous zones of exposure.
Now, more than 35 years later the software design for medical equipment have changed with safer user interface design and built in defensive safety critical error detection & checks. Because making the user interface easy can sometimes compromise the safety.