You can take up to 15 points of radiation poisoning with no negative effects until 10 points. While radiated, you may regenerate crippled of destroyed limbs. You also receive a +2 bonus to healing skill.
This was given to Markas, whose body had undergone a considerable amout of radiation poisoning while conducting an experiment for Moira on the effects of radiation on the human body. After being treated by Moira, Markas discovered that he had built up some sort of mild immunity to the radiation.