Just another plug for the comp.risks digest. This digest from the ACM Committee on Computers and Public Policy has been moderated continuously by Peter G. Neumann since its inception in 1985. If you don't frequent Usenet like you used to in the 80s, the web archive is here:

http://catless.ncl.ac.uk/Risks

The Therac-25 was discussed here many times, starting with Vol. 3 Issue 9:

http://catless.ncl.ac.uk/Risks/3.09.html#subj2