Um, no. X-rays are a much SHORTER wavelength than visible light and therefore attenuate MORE than light. X-rays have a wavelength of between .01 nm to 10 nm. Visible light falls between 380 nm and 740 nm. X-rays are readily absorbed by air. That is why large nuclear weapons are relatively safe from a radiation standpoint. With a smaller explosion you can be safe from the blast and heat but still receive a deadly dose of radiation. With larger yield weapon you would most likely be killed by the blast or thermal energy well outside the range of deadly radiation. Absorption of xray radiation by the atmosphere is actually responsible for much of the thermal energy and blast effects in a nuclear weapon. If you detonated one in space you would get little to no blast but you would get a pulse of heat and a huge dose of radiation.

I believe you are referring to the accidents with the THERAC-25? http://en.wikipedia.org/wiki/Therac-25

The Therac-25 was a radiation therapy machine produced by Atomic Energy of Canada Limited (AECL) after the Therac-6 and Therac-20 units (the earlier units had been produced in partnership with CGR of France). It was involved in at least six accidents between 1985 and 1987, in which patients were given massive overdoses of radiation, approximately 100 times the intended dose.[2]:425 These accidents highlighted the dangers of software control of safety-critical systems, and they have become a standard case study in health informatics and software engineering.

Much more detailed write-up on the accidents. http://sunnyday.mit.edu/papers/therac.pdf