Comparison of head and body organ doses in CT

We compare head and body organ doses received by adult patients undergoing whole body scans operated using the same technique factors. Dosimetry data were obtained for six CT scanners (16 and 64 slice) from four vendors. Organ doses were obtained using the ImPACT CT dose software package for an adult male, together with the corresponding head and body CTDI(w). Our data provide a link between the CTDI doses generated on most commercial scanners for each clinical CT examination and doses to organs and tissues within the directly irradiated region of an adult patient. The average numerical ratio of the brain dose to the head phantom CTDI(w) is 0.84+/-0.05, the average ratio of the lung dose and liver dose to the body phantom CTDI(w) is 1.65+/-0.05 and 1.48+/-0.05, respectively. When scanned under identical conditions, lung doses are similar to brain doses, and liver doses are only approximately 10% lower. By comparison, the average body to head CTDI(w) ratio was 0.49+/-0.06, which erroneously implies that doses to organs in the head are twice those of doses to organs in the body at the same techniques. Two CT dosimetry phantom sizes are therefore not required, and our findings support the need to reassess the role, if any, of current cylindrical acrylic dosimetry phantoms.