Exposure to moderate to high doses of ionizing radiation is known to increase the risk of cancer, especially following childhood exposure. However, studies suggest that excess cancer risk can occur even from low doses of ionizing radiation. For X-rays and γ-rays, there is good evidence of increased cancer risk at acute doses exceeding 50 mSv and reasonable evidence for increased risk above approximately 10 mSv (Shah et al., 2012). For protracted exposures, good evidence suggests increased risk above 100 mSv, with reasonable evidence above approximately 50 mSv (Brenner et al., 2003).