I'm not sure. Most software (by orders of magnitude) is not critical software like the software running that X-ray machine. In general, if your software fails, a page loads too slow, or a report comes with lots of NaN's, or some batch job does not run at the right time, and someone needs to start it manually, etc. The cases where someone dies because of a software quality issue are very rare, and the developers working on that type of software know who they are and what their duties are (I hope).