The radiation dose of spiral CT is the same as that of normal CT. The radiation dose varies according to the site, the scope of the scan, and the exposure time. The required radiation dose is projected according to the site and exposure time during the examination. Since the lungs contain more air and the tissue density is low, the machine will calculate the amount of radiation needed based on the size of the tissue density, so the CT dose for the lungs is lower. Since the skull is harder and denser, the CT machine detects with a higher milliamp output and a higher amount of radiation.