CT scanning is a relatively high dose procedure that is becoming much more common worldwide. In the mid-1990s, CT scanning accounted for about 4% of procedures and about 40% of the collective dose in diagnostic radiology. With the advent of helical, fluoroscopic, and multi-slice techniques the dose per procedure has not diminished and the use of CT has increased even more. In large hospitals, CT scanning now accounts for about 15% of procedures and 75% of the diagnostic radiation dose received by patients. When multiple CT scans are conducted on the same patient, the absorbed doses are in the range at which small but statistically significant increases in cancer have been found in the atomic bomb survivors.