Answer to Question #4319 Submitted to "Ask the Experts"

If you have a chest, abdominal, and pelvic CT all in one scan, would this be considered as a whole-body scan or how would this relate to the dose per organ ratio? If a whole-body scan is 1 rad I am assuming that all of these together would not be more? I had two of these tests done within two months of each other. Please advise on how much total radiation dose this would be.

There are several methods of expressing dose from CT scans. The most useful and most widely used is effective dose, which is a way of expressing an equivalent uniform whole-body dose. Published values of effective dose from CT of chest, abdomen, or pelvis are generally on the order of 7-8 millisievert per exam. The sievert is the metric system unit of radiation equivalent dose (1 sievert = 100 rem). The dose for an exam is equal to the dose per CT slice multiplied by the number of slices. Thus, the effective dose for the three exams is equal to the sum of each exam independently, or about 20-25 millisievert (2-2.5 rem). For x-ray exposure, the equivalent dose in sievert (rem) is numerically equal to the dose in gray (rad). In any event, the benefit you received from your CT exams clearly outweighs any potential radiation effect.

S. Julian Gibbs, DDS PhD