Gray: Ionizing radiation is measured by the amount of energy the body absorbs, and the unit of measurement is the Gray (Gy) Other units include the centiGray (cGy) and the rad. One cGy equals one rad. One hundred cGy equals one Gray. For example, 60 Gy equals 6,000 cGy equals 6,000 rad. (The term “rad” is no longer used, but it is still found in the medical literature).